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Heat induced denaturation, aggregation and gelation of almond proteins in skim and full fat almond milk
Abstract
The effect of thermal treatment (45-95 ⁰C for 30 minutes) on the structure of almond milk proteins was assessed, as the unfolding and association of these proteins in response to heat is not well understood. Above 55 ⁰C, protein surface hydrophobicity and particle size increased and alpha helical structure decreased, reducing the stability of skim or full fat milk. Fractal protein clusters were observed at 65-75 ⁰C and weakly flocculated gels with a continuous protein network occurred at 85-95 ⁰C, resulting in gels with high water holding capacity and a strength similar to dairy gels. The presence of almond fat increased gel strength but led to a more heterogenous microstructure, which may be improved by homogenisation. Elasticity could also be increased with protein concentration. This study improves our understanding of the heat stability of almond milk proteins and indicates their potential as a gelling ingredient for vegan and vegetarian products.
... A hypothesis for such an incomplete extraction rate could be advanced, about a dynamical balance between the extraction and degradation rate of the proteins during the hybrid HC and thermal extraction processes. Such hypothesis is supported by previous research, which showed that partial heat-induced almond protein denaturation occurs already at temperatures between 45 • C and 55 • C and at an accelerated pace above 65-75 • C, while such proteins, although water soluble and thus in principle easily extractable by HC processes, are embedded in oleosins surrounding the oil droplets, making them harder to extract [51]. The matching of the obtained protein concentration levels with the commercial product also appears to support the above hypothesis, which might represent a general limitation in the production of almond beverages. ...
... However, it is noticeable that the extraction rate of proteins in test MGP3 was only slightly lower than in test MGP1, which supports the above-presented hypothesis about the complex extraction/denaturation kinetics, i.e., late extraction of proteins in MGP3 might have limited their denaturation. Further experiments and theoretical research are recommended on this topic, for example to investigate the effects of isothermal steps on the extraction rate of nutritional compounds, especially at temperatures below the above-mentioned threshold for protein denaturation (45-55 • C) [51], or by using reactors able to generate more aggressive and effective cavitation regimes [37]. ...
... On the sensorial side, beyond the subjective judgment of the authors about the good taste of both the beverage-like extracts (tests MFP1 and MGP1) and the concentrated extract (test MGP3), the retention of the kernel skin in the latter test did not alter too much the usual creamy white color that consumers are used to, as shown in Figure 8. [51], or by using reactors able to generate more aggressive and effective cavitation regimes [37]. On the sensorial side, beyond the subjective judgment of the authors about the good taste of both the beverage-like extracts (tests MFP1 and MGP1) and the concentrated extract (test MGP3), the retention of the kernel skin in the latter test did not alter too much the usual creamy white color that consumers are used to, as shown in Figure 8. Overall, the possibility of generating high concentration aqueous extracts from whole almond seeds, ready for further dilution and production of almond beverages, by means of HC-based processes as a single-unit operation, was successfully demonstrated, which is another original result of this study. ...
Perceived as a healthy food, almond beverages are gaining ever-increasing consumer preference across nonalcoholic vegetable beverages, ranking in first place among oilseed-based drinks. However, costly raw material; time and energy consuming pre-and posttreatments such as soaking, blanching and peeling; and thermal sterilization hinder their sustainability, affordability and spread. Hydrodynamic cavitation processes were applied, for the first time, as a single-unit operation with straightforward scalability, to the extraction in water of almond skinless kernels in the form of flour and fine grains, and of whole almond seeds in the form of coarse grains, up to high concentrations. The nutritional profile of the extracts matched that of a high-end commercial product, as well as showing nearly complete extraction of the raw materials. The availability of bioactive micronutrients and the microbiological stability exceeded the commercial product. The concentrated extract of whole almond seeds showed comparatively higher antiradical activity, likely due to the properties of the almond kernel skin. Hydrodynamic cavitation-based processing might represent a convenient route to the production of conventional as well as integral and potentially healthier almond beverages, avoiding multiple technological steps, while affording fast production cycles and consuming less than 50 Wh of electricity per liter before bottling.
... A hypothesis for such incomplete extraction rate could be advanced, about a dynamical balance between the extraction and degradation rate of the proteins, both caused by the HC processes. Such hypothesis is supported by previous research, which showed that partial heat-induced almond protein denaturation occurs already at temperatures between 45°C and 55°C and at an accelerated pace above 65-75°C, while such proteins, although water soluble and thus in principle easily extractable by HC processes, are embedded in oleosins surrounding the oil droplets, making them harder to extract [54]. The matching of the obtained protein concentration levels with the commercial product also appears to support the above hypothesis, which might represent a general limitation in the production of almond beverages. ...
... However, it is noticeable that the extraction rate of proteins in test MGP3 was only slightly lower than in test MGP1, which supports the above hypothesis about the complex extraction/denaturation kinetics, i.e., late extraction of proteins in MGP3 might have limited their denaturation. Further experiments and theoretical research are recommended on this topic, for example to investigate the effects on the extraction rate of nutritional substances of isothermal steps, especially at temperatures below the above-mentioned threshold for protein denaturation (45-55°C) [54], or using reactors able to generate more aggressive and effective cavitation regimes [22]. ...
... On the sustainability side, based on Figure 2(b), the consumption of specific energy of about 100 Wh/L at the end of the test MGP3 (concentration of 18%) would translate, after dilution, in a specific energy consumption for the almond beverage (concentration around 8%) of 50 Wh/L or even lower. 19 of 26 Finally, the critical gelation temperature, estimated at 87.5°C, while representing an upper limit for the production of acceptable almond beverages or concentrated extracts ready for dilution, also by means of HC-based processes, might offer the chance to generate new products by means of the same HC processes, such as almond tofu or cheese, which require higher concentrations of raw almond material than used for the manufacturing of commercial beverages [54]. ...
Almond beverages are gaining ever-increasing consumer preference in the growing market of non-alcoholic vegetable beverages, ranking in first place among oilseed-based drinks, mainly due to the perceived healthy benefits. However, the high cost of the raw material, time and energy consuming pre-treatments such as soaking, blanching and peeling, and post-treatments such as thermal sterilization, leading also to the loss of valuable macronutrients and micronutrients, hinder the sustainability, affordability and spread of almond beverages. Hydrodynamic cavitation processes were applied, as a single-unit operation, to the extraction in water of almond skinless kernels in the form of flour and fine grains, and to whole almond seeds in the form of coarse grains, up to high concentrations. The results showed full compliance with a high-end commercial product and with the expected levels based on the properties of the raw materials. The concentrated extract obtained from whole almond seeds showed a comparatively much higher antiradical activity, likely due to the contribution of the almond kernel skin. In conclusion, hydrodynamic cavitation could represent a convenient alternative processing route to the production of conventional and new integral almond beverages, avoiding multiple and costly technological steps, while affording fast production cycles of potentially healthier beverages.
... This indicates that the RP and AP proteins underwent greater structural changes due to the physical treatment compared to ISP and PP. The pH of almond milk derived from an almond and water mixture with a 1:4 ratio was 6.2 without the physical treatment [14], and the pH of homogenized/sterilized almond milk was 6.64 [15]. Similar to the aforementioned research results, it is believed that the increase in pH of AP is due to the significant structural changes of the protein caused by the pasteurization and homogenization processes. ...
... For pH 4.5 and below, the buffering capacity of the treated group is lower than the untreated group. Devnani et al. (2020) [14] reported that the stability of almond milk decreases at 55 °C and higher as almond milk proteins undergo an increase in protein surface hydrophobicity and molecular size and a decrease in alpha helix structures. Such an increase in surface hydrophobicity has been reported to be due to the exposure of the internal hydrophobic regions of amandine, the storage protein of almonds, as the protein molecule unfolds [16]. ...
... For pH 4.5 and below, the buffering capacity of the treated group is lower than the untreated group. Devnani et al. (2020) [14] reported that the stability of almond milk decreases at 55 °C and higher as almond milk proteins undergo an increase in protein surface hydrophobicity and molecular size and a decrease in alpha helix structures. Such an increase in surface hydrophobicity has been reported to be due to the exposure of the internal hydrophobic regions of amandine, the storage protein of almonds, as the protein molecule unfolds [16]. ...
Effects of plant proteins and dietary fibers on the physical properties of stirred soy yogurt were investigated. Buffering capacity against lactic acid was not affected by the protein concentration for any of the four proteins that were examined: isolate soy protein (ISP), pea protein (PP), rice protein (RP), and almond protein (AP). Three proteins other than AP exhibited an increase in buffering capacity (dB/dPH) following a physical treatment, whereas AP saw a decrease in buffering capacity. Furthermore, physically treated PP revealed a significant increase in viscosity, reaching up to 497 cp in the pH 6.0~6.2 range during the titration process. Following fermentation, PP produced the highest viscosity and coagulum strength with no syneresis. In the case of dietary fiber, Acacia Fiber (AF) was completely dissolved in the solvent and did not affect the physical properties of the fermented coagulum. Soy fiber (SF) was also not suitable for fermented milk processes because precipitation occurred after the physical treatment. In the case of citrus fiber (CF), however, syneresis did not occur during storage after the physical treatment, and the viscosity also increased up to 2873 cP. Consequently, PP and CF were deemed to be a suitable plant protein and dietary fiber for stirred soy yogurt, respectively.
... However, most commercial almond-based gels have low protein content (<2.3%) compared with dairy yoghurts (>2.7% protein) (Zhao et al., 2021). The main technical reason for the low protein content in commercial almond-based gels could be that the almond protein has weak hydrophobicity and low molecular weight (basically 20-22 kDa, acidic polypeptides 42-46 kDa), resulting in poor protein dispersibility in almond emulsion and unstable gel formation in almond gel (de Souza et al., 2020;Devnani et al., 2020;Shi et al., 2020). Functional properties such as solubility, gelation, viscosity, foamability, water retention ability and oil binding capacity of almond proteins significantly affect the quality of almond-based foods (Sze-Tao and Sathe, 2000). ...
... That means they can form a gel structure (Klost et al., 2020) after incorporation of the non-hydrolysed protein. The non-hydrolysed protein present in the control sample 13 were far denser in some regions based on band position: the region 65-70 kDa refers to the major protein amandin, consistent with Devnani et al. (2020) where amandin appeared at band 60 kDa in their almond milk samples; the bands around 35 kDa should be the known acidic polypeptides of amandin (38-42 kDa), while the band around 20 kDa corresponds to the basic polypeptides (20-22 kDa) that is associated with disulphide bonds (Sathe, 1992). Other rare bands between 90 and 240 kDa at very low levels need further study. ...
Protein inadequacy is the major problem for most plant-based dairy yoghurt substitutes. This study investigated three limited degree of hydrolysis (DH: 1%, 5%, and 9%) of almond protein and the combined effect of DH and hydrolysed almond protein (HP) to non-hydrolysed almond protein (NP) ratios (HP/NP: 40:60, 20:80, 10:90 and 5:95) on the physicochemical properties of resulting fermentation induced almond-based gel (yoghurt). The gel microstructure, particle size, firmness, pH, water holding capacity (WHC), lubrication, flow, and gelation characteristics were measured and associated with the DH, composition, and SDS-PAGE results. The results show significant differences in gel samples with the same HP/NP (40:60) ratio of protein but different protein DH. A higher DH (9%) resulted in samples with lower hardness (6.03 g), viscosity (0.11 Pa ·s at 50 s-1), cohesiveness (0.63) and higher friction (0.203 at 10 mm/s) compared to sample with 1% DH with higher hardness - 7.34 g, viscosity at 50 s⁻⁻¹ - 0.16 Pa ·s, cohesiveness - 0.86 and friction at 10 mm/s - 0.194. Comparing samples with the same DH (5%) but different HP/NP ratios showed smaller coarse microgel particles (21.36 μm) and lower hardness (7.17 g), viscosity (0.14 Pa ·s at 50 s⁻⁻¹) and friction value (0.189 at 10 mm/s) in samples with high HP/NP (40:60) compared to sample with low HP/NP (5:95) that contained significantly large coarse microgel particles (34.61 μm) with the gel being very hard (9.38 g), highly viscous (0.32 Pa ·s at 50 s⁻⁻¹), and less lubricating (0.220 at 10 mm/s).
... Accordingly, the more intense the thermal treatment is, the more protein modification may occur. These modifications could be protein aggregation, amino acid reduction, and protein denaturation, which could affect the amines availability for the crosslinking with genipin and, consequently, reducing the formation of blue compounds ( Bogahawaththa et al., 2018( Bogahawaththa et al., , 2017Devnani et al., 2020 ). ...
... Therefore, milk components are not thermally affected in the drying process. The milk proteins are most affected during the SD due to the whey protein and casein aggregation ( Smithers and Augustin, 2012 ;Devnani et al., 2020 ). ...
The production of an innovative food ingredient obtained from unripe Genipa Americana L. pulp and milk was studied in this paper. Natural blue compounds were produced from the crosslinking between genipin and milk proteins. They are a promising ingredient for the natural food colorant sector. In this way, this paper aimed to evaluate the impact of heat treatments applied to raw milk on the production of blue compounds. Thermal treatments could change the milk protein conformation and the exposition of their amine groups affecting the crosslinking with genipin. For this, raw milk was subjected to different thermal treatments such as low-temperature and long-time (LTLT; 60°C/30 min), high-temperature and short-time (HTST; 72°C/15 s), ultra-high temperature (UHT; 145°C/2 s), and spray drying (SD; inlet and outlet temperature: 165 and 79°C, respectively). Thermally treated milk samples were used as solvents for the genipin extraction from unripe genipap pulp and suppliers of proteins to produce blue compounds. Blue colorants milk-based were compared concerning their FTIR spectra, free-genipin content, and color attributes. High temperatures impacted protein conformation, reducing the number of primary amines available for crosslinking. Free-genipin content after the reaction step was a good crosslinking indicator. The HTST-treated milk produced the bluest colorant due to its higher number of primary amines available to react with genipin. Our findings demonstrated that the heat treatment applied to raw milk could influence the production of blue compounds. These results are useful for the enhancement of the manufacturing process of natural blue food colorants.
... These modifications include protein aggregation, decreased amino acid content, and denaturation. These modifications have the potential to impact the presence of amines for cross-linking with GNP (Bogahawaththa, Buckow, Chandrapala, & Vasiljevic, 2018;Bogahawaththa et al., 2017;Devnani, Ong, Kentish, & Gras, 2020). He et al. (2023) have found that GNP cross-linking significantly affected the gelling properties of ginkgo seed protein isolate. ...
... Almond, oat, and rice milk contain six times fewer proteins than cow milk [16]. Almond milk is rich in fats (44-61%), low in carbohydrates (2-8%), and possesses hexameric globulins (16-26%) of molecular weight around 275-450 kDa [50]. Almond milk is used as an alternative milk beverage for people with cow's milk allergy and lactose intolerance [44]. ...
There is a growing demand for nutritional, functional, and eco-friendly dairy products, which has increased the need for research regarding alternative and sustainable protein sources. Plant-based, single-cell (SCP), and recombinant proteins are being explored as alternatives to dairy proteins. Plant-Based Proteins (PBPs) are commonly used to replace total dairy protein. However, PBPs are generally mixed with dairy proteins to improve their functional properties, which makes them dependent on animal protein sources. In contrast, single-Cell Proteins (SCPs) and recombinant dairy proteins are promising alternatives for dairy protein replacement since they provide nutritional components, essential amino acids, and high protein yield and can use industrial and agricultural waste as carbon sources. Although alternative protein sources offer numerous advantages over conventional dairy proteins, several technical and sensory challenges must be addressed to fully incorporate them into cheese and yogurt products. Future research can focus on improving the functional and sensory properties of alternative protein sources and developing new processing technologies to optimize their use in dairy products. This review highlights the current status of alternative dairy proteins in cheese and yogurt, their functional properties, and the challenges of their use in these products.
... About 65-70% of the total protein in almonds comes from globulin protein (amandin-storage protein), which has a hexameric structure linked to acidic and basic polypeptides by disulphide bonds. This results in almond yogurt having higher gel strength and greater water retention (Wolf & Sathe, 1998;Kshirsagar et al., 2011;Devnani et al., 2020;Gul et al., 2017). The impact of thermal treatment and microbial fermentation on the structure and physical-chemical properties of almond proteins is not well understood, but higher heat treatments (85-90 • C) are thought to lead to higher denaturation and gelation, creating protein networks that trap fat droplets. ...
... Conversely, overhigh temperature could cause protein denaturation and aggregation, increase β-sheets content, and reduce emulsion stability (Zhao et al., 2016). Significant changes in structure and functional properties of proteins after roasting have been found in other nuts, such as cashew nuts (Yan et al., 2021), peanuts (Zhao et al., 2009) and almonds (Devnani et al., 2020). Ines et al. (2021) derived a structure-function relationship by studying structure and functional properties of two black cumin seed isolate proteins. ...
Effects of roasting treatment on functional properties and structure of pine kernel protein from two grafted species: Pinus koraiensis (PK) and Pinus sylvestris var. (PKS) were evaluated by analysis of SDS‐PAGE, FTIR, fluorescence spectrum, solubility, emulsifying properties, etc. The results showed that roasting improved functional properties of PK and PKS. Structure analysis elucidated that conformational changes of tertiary structure, occurrence of unfolded protein structure, and enhancement in α‐helix and random coil structures. For PK, solubility, emulsifying and oil holding capacity (OHC) were the highest at 150 °C, 20 min. PKS had the highest emulsification and OHC at 150 °C, 10 min. The improvements in functional properties of PK and PKS should be attributed to the influence of intramolecular intergroup forces on secondary and tertiary structures, which resulted in higher surface charges and reduced turbidity. This study provided a reference for moderating quality properties of two kinds pine kernel.
... Solutions were diluted before measurement to give a final concentration of 0.3 mg/ml. The path length was 1 mm, the spectral resolution was 1 nm, data collection interval and bandwidth were 1 s and 1 nm, respectively (Devnani et al. 2020). Samples were prepared in duplicate and each recorded spectrum was an average of 3 scans. ...
Amyloid crystals, a form of ordered protein aggregates documented relatively recently, have not been studied as extensively as amyloid fibres. This study investigates the formation of amyloid crystals with low frequency ultrasound (20 kHz) using β-lactoglobulin, as a model protein for amyloid synthesis. Acoustic cavitation generates localised zones of intense shear, with extreme heat and pressure that could potentially drive the formation of amyloid structures at ambient bulk fluid temperatures (20 ± 1 °C). Thioflavin T fluorescence and electron microscopy showed that low-frequency ultrasound at 20 W/cm ³ input power induced β-stacking to produce amyloid crystals in the mesoscopic size range, with a mean length of approximately 22 µm. FTIR spectroscopy indicated a shift towards increased intermolecular antiparallel β-sheet content. An increase in sonication time (0–60 min) and input power (4–24 W/cm ³ ) increased the mean crystal length, but this increase was not linearly proportional to sonication time and input power due to the delayed onset of crystal growth. We propose that acoustic cavitation causes protein unfolding and aggregation and imparts energy to aggregates to cross the torsion barrier, to achieve their lowest energy state as amyloid crystals. The study contributes to a further understanding of protein chemistry relating to the energy landscape of folding and aggregation. Ultrasound presents opportunities for practical applications of amyloid structures, presenting a more adaptable and scalable approach for synthesis.
Graphical abstract
... In addition, regarding the byproducts obtained after centrifugation, the BM-D fraction showed an important content (about 57/100 g d.w.), probably due in part to the effect of the thermal denaturation of some proteins and the increased hydrophobicity [24]. This fact was observed in soy and almond milk when they were subjected to moderate heat treatments (around 60-80 • C), showing lower precipitation and protein denaturation than those produced when they were treated at high temperatures (over 85 • C) [25,26]. In the case of the BM-F fraction, it had a predominance of lipid content (about 80/100 g d.w.), being related to the high-fat content coming from the raw material. ...
The consumption of plant-based beverages is a growing trend and, consequently, the search for alternative plant sources, the improvement of beverage quality and the use of their by-products, acquire great interest. Thus, the purpose of this work was to characterize the composition (nutrients, phytochemicals and antioxidant activity) of the Brazil nut (BN), its whole beverage (WBM), water-soluble beverage (BM-S), and its by-products of the beverage production: cake, sediment fraction (BM-D), and fat fraction (BM-F). In this study, advanced methodologies for the analysis of the components were employed to assess HPLC-ESI-QTOF (phenolic compounds), GC (fatty acids), and MALDI-TOF/TOF (proteins and peptides). The production of WBM was based on a hot water extraction process, and the production of BM-S includes an additional centrifugation step. The BN showed an interesting nutritional quality and outstanding content of unsaturated fatty acids. The investigation found the following in the composition of the BN: phenolic compounds (mainly flavan-3-ols as Catechin (and glycosides or derivatives), Epicatechin (and glycosides or derivatives), Quercetin and Myricetin-3-O-rhamnoside, hydroxybenzoic acids as Gallic acid (and derivatives), 4-hydroxybenzoic acid, ellagic acid, Vanillic acid, p-Coumaric acid and Ferulic acid, bioactive minor lipid components (β-Sitosterol, γ-Tocopherol, α-Tocopherol and squalene), and a high level of selenium. In beverages, WBM had a higher lipid content than BM-S, a factor that influenced the energy characteristics and the content of bioactive minor lipid components. The level of phenolic compounds and selenium were outstanding in both beverages. Hydrothermal processing can promote some lipolysis, with an increase in free fatty acids and monoglycerides content. In by-products, the BM-F stood out due to its bioactive minor lipid components, the BM-D showed a highlight in protein and mineral contents, and the cake retained important nutrients and phytochemicals from the BN. In general, the BN and its beverages are healthy foods, and its by-products could be used to obtain healthy ingredients with appreciable biological activities (such as antioxidant activity).
... The apparent viscosity at a shear rate 50 s − 1 significantly increased from 0.03 Pa s in AY1 to 0.11 Pa s in AY4 (Table 3), due to the stronger protein-protein interactions formed during fermentation. Moreover, the heat treatment during the preparation of almond yoghurt causes protein denaturation that resulted in an increased water-binding capacity (Devnani et al., 2020) thus producing higher viscosity yoghurt. Similar results were obtained by Kizzie-Hayford et al. (2016) who found that enriching base tigernut milk with whey protein (1-3%) improved the apparent viscosity of the final yoghurt. ...
The influence of the protein, fat and sugar in almond milk on the formation of the acidic gel was investigated by determining their physicochemical and microstructural properties. The protein, fat and sugar in the almond milk were varied from 2% to 6%, 0.8%–7% and 0.6%–7%, respectively and fermented using Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophiles cultures to form a gel structure. Both protein and fat increased the gel strength, viscosity (stirred gel) and lightness of almond yoghurts as the concentration increased. The addition of protein content increased the cohesiveness (from 0.70 to 1.17), water holding capacity (from 28.75% to 52.22%) and D4,3 value of particle size (from 32.76 μm to 44.41 μm) of almond yoghurt. Fat reduction decreased the firmness (from 6.56 g to 4.69 g), D4,3 value (from 88.53 μm to 18.37 μm), and water holding capacity (from 48.96% to 27.66%) of almond yoghurt. With sugar addition, almond yoghurt showed increased adhesiveness, decreased lightness and a low pH, with no significant difference in firmness, particle size, and flow behaviour. The confocal images provided evidence that the fortified protein contents homogeneously entrapped fat globules resulting in a more stable gel network and increased fat content led to large fat globule formation resulting in a harder gel network, while the added sugar did not significantly affect the gel network. The results suggested that the protein fortification enhances the texture of almond yoghurt. The fat content of 7% with 3.5% protein showed poor consistency and gel strength of yoghurt. Sugar mainly contributed to bacterial metabolism during fermentation.
... but it usually contains a large amount of sugar as well as being low in protein whence methionine is the limiting amino acid [31]. It is indicated to reduce blood cholesterol levels used in postoperative processes for its high nutritional value, its easy digestion helps diarrhea and vomiting as it is a good regulator of intestinal mobility, indicated for pregnant women, nursing mothers to combat nervous diseases and for anemia, improves the nervous system problem [32]. ...
... SLS has also been used to study the impact of processing methods, such as thermal processing and highpressure treatment, on the particle size in almond milk (Dhakal et al., 2016). The authors found that both processing methods increased the particle size substantially, which was mainly attributed to their impact on protein unfolding and aggregation (Devnani et al., 2020). The same method has been used to compare the particle sizes of different kinds of commercially available plant-based milks, including soy, oat, quinoa, and rice milks (Makinen et al., 2015). ...
The food industry is creating a diverse range of plant-based alternatives to dairy products, such as milks, creams, yogurts, and cheeses due to the increasing demand from consumers for more sustainable, healthy, and ethical products. These dairy alternatives are often designed to mimic the desirable physicochemical, functional, and sensory properties of real dairy products, such as their appearance, texture, mouthfeel, flavor, and shelf-life. At present, there is a lack of systematic testing methods to characterize the properties of plant-based dairy alternatives. The purpose of this review is to critically evaluate existing methods and recommend a series of standardized tests that could be used to quantify the properties of fluid plant-based milk alternatives (milk and cream). These methods could then be used to facilitate the design of milk alternatives with somewhat similar attributes as real dairy milk by comparing their properties under standardized conditions. Moreover, they could be used to facilitate comparison of the properties of milk alternatives developed in different laboratories.
... A volume of 10 μl of each of fast green FCF solution (1 mg/ml in MilliQ water, Sigma-Aldrich, St. Louis, U.S.A.) and Nile red solution (1 mg/ml in 100% dimethyl sulfoxide, Sigma-Aldrich, St. Louis, U.S.A.) was added to 480 μl of the sample that included protein and fat particles. The stained sample was diluted 1:5 with agarose solution (40 • C, 0.25 g/50 ml Milli Q water) to reduce particle movement due to Brownian motion, as shown in previous literature (Devnani, Ong., Kentish, & Gras, 2020;Lopez, Madec, & Jimenez-Flores, 2010). The fat specific stain Nile red only stained the fat core of the MFG and did not provide any information about the MFGM (Ong et al., 2010a). ...
A B S T R A C T
This study presents the design and characterisation of casein−whey protein suspensions (8.0/10.0% (w/w) casein and 2.0/2.5% (w/w) whey protein) mixed with dairy fat (1.0, 2.5 and 5.0% (w/w) total fat) processed via the pH−temperature-route in preparation for 3D-printing. Mechanical treatment was applied to significantly decrease the particle size of the milk fat globules and increase surface area, creating small fat globules (<1 μm) covered with proteins, which could act as pseudo protein particles during gelation. Different proteins covered the fat globule surface after mechanical treatment, as a result of differences in the pH adjusted just prior to heating (6.55, 6.9 or 7.1). The protein-fat suspensions appeared similar by transmission electron cryogenic microscopy and the zeta-potential of all particles was unchanged by the heating pH, with a similar charge to the solution (∼−20 mV) occurring after acidification (pH 4.8/5.0) at low temperatures (2°C). A low heating pH (6.55) resulted in increased sol−gel transition temperatures (G՛ = 1 Pa) and a decreased rate of aggregation for protein−fat suspensions. A higher heating pH (6.9 and 7.1) caused an increased rate of aggregation (aggregation rate ≥ 250 Pa/10 K), resulting in materials more promising for application in extrusion-based printing. 3D-printing of formulations into small rectangles, inclusive of a sol−gel transition in a heated nozzle, was conducted to relate the aggregation rate towards printability.
Malnutrition and micronutrient deficiencies are observed among people in many developing countries. The high cost of cow's milk and poverty make it difficult for people to access nutritious food. For this reason, low-cost foods that can be an alternative to cow's milk are important. In addition, the fact that cow's milk causes lactose intolerance, high cholesterol, constipation and bloating in some individuals has led people to other alternatives. Apart from these, alternatives for vegan individuals have begun to be considered. All these reasons have increased the demand for alternative milk of plant origin worldwide. Plant-based milks have been the subject of research with different names in the literature. For example: vegetable milk, non-dairy milk, imitation milk, dairy substitute. This review is focused on comparing nutrient composition of cow's milk and plant-based milk alternatives.
Bitki esaslı süt benzeri içecekler uluslararası gıda pazarında son yıllarda en hızlı yükselen ürün gruplarından biridir. Bitki esaslı süt benzeri içecekler görünüş ve kıvam bakımlarından inek sütüne benzeyen ve bitkisel bir kaynağın sulu ekstreleri olan formüle edilmiş içeceklerdir. Bu içeceklerin özellikleri, hammaddelerine ve özellikle de formülasyonlarına göre önemli ölçüde değişkenlik göstermektedir. Bununla birlikte bitki esaslı süt benzeri içeceklerin genel olarak inek sütü gibi hayvansal süt kaynaklarından önemli farklılıkları bulunmaktadır. Bu çalışmada ticari olarak mevcut olan ve görece daha yaygın olarak tüketilen bitki esaslı süt benzeri içeceklerin besinsel içerikleri, üretim aşamaları ve sağlık üzerine etkileri gibi çeşitli özellikleri derlenmiştir.
Consumers are increasingly looking for new plant-based alternatives to substitute animal proteins in their diets but for some applications it can be difficult to achieve the desired product microstructure using only plant proteins. One approach to facilitate structuring is to mix these plant-based ingredients with a polysaccharide. Here, the phase behaviour and microstructure of quinoa protein isolate (QPI) in mixture with maltodextrin (MD) of two dextrose equivalents (DE 7 and 2) were investigated. The binodals of both QPI-MD phase diagrams showed an atypical shape, where the concentration of MD in the QPI-rich phase and of QPI in the MD-rich phase increased with overall biopolymer concentration. Molecular weight distribution and microstructure analyses revealed that both maltodextrins fractionated between the phases and were probably entrapped within the volume-spanning protein network in the QPI-rich phase, indicating a depletion flocculation mechanism of phase separation. The pre-heating of QPI and the removal of salt from the systems resulted in similarly atypical phase diagrams. The approach presented contributes to our understanding of the phase behaviour of mixtures between plant proteins and polysaccharides, while the results suggest that the formulation of plant-based products of predictable properties may be more challenging than anticipated.
In this study, gastric digestion of isocaloric and iso-macronutrient cow milk, almond milk and oat milk were compared in rats euthanized at different post-feeding times. The cow milk separated into a curd phase and a liquid phase in the rat stomach. This coagulation of the cow milk led to higher (P < 0.05) protein and lipid retention in the stomach compared with almond milk and oat milk. Almond milk oil bodies aggregated, creamed and rapidly layered in the stomach. This induced a faster (P < 0.05) gastric emptying of proteins (T1/2 = 36 min) compared with cow milk (T1/2 = 89 min) and oat milk (T1/2 = 55 min), and a slower gastric emptying of almond lipids than of almond proteins. In contrast, no significant physical change during the digestion of oat milk was found, with both the proteins and the lipids being steadily emptied from the stomach. This in vivo study provides information on the gastric digestion and emptying (and thereby nutritional characteristics) of plant-based milks compared with animal-based milks, that will be useful for the design of novel plant-based drinks.
There is an increasing trend today towards plant-based diets in western society, often resulting in milk restriction. In the case of very young children, the direct substitution of milk by other foods, without proper nutritional advice, may lead to a lack of nutrients and hence to growth and development alterations. This study focuses on the nutritional assessment of various commercially available plant-based drinks, to determine their adequacy as alternatives to ruminant milk, in relation to the nutritional requirements of toddlers (1–3 years old), and to establish whether other sources of nutrient supplementation may be needed, as well as any other possible positive and /or negative health effects associated to their consumption. A sample of 179 commercial plant-based drinks (almond, coconut, hemp, oat, rice, soy, tigernut) were chosen and their nutrient contents were compared to the EFSA nutrient reference values for toddlers. The scientific literature on the presence of bioactive and/or undesirable compounds was reviewed.
None of the plant-based drinks studied should be considered as a milk substitute, since they are different food products with a different composition. However, from the results obtained, the best choice for toddlers who do not consume milk would be to consume at least 250 mL/day of fortified soy drink (for its higher amount and quality of protein, polyunsaturated fatty acids and phytosterols), and always in the context of a carefully-balanced diet. Almond, hemp or oat drinks are other alternatives that can be used in combination or for soy-allergic toddlers.
The key nutrients that should be fortified in plant-based drinks are: vitamins A and B12, calcium, zinc and iodine, as they represent the most significant nutritional differences with milk; vitamin D would also be desirable. Of these, vitamins A, B12, D and calcium, are easily found in many commercial plant-based drinks on the Spanish market (most frequently in soy drinks), unlike iodine and zinc, which were not added to any. Given the fish restriction in vegetarians/vegans and the fact that plant-based drinks provide high amounts of phytates and tannins, which act as antinutrients, a good strategy for the industry would be to fortify plant-based drinks with iodine and zinc to improve the nutritional value of products aimed to vegetarians/vegans.
Microscopy is often used to assist the development of cheese products, but manufacturers can benefit from a much broader application of these techniques to assess structure formation during processing and structural changes during storage. Microscopy can be used to benchmark processes, optimize process variables, and identify critical control points for process control. Microscopy can also assist the reverse engineering of desired product properties and help troubleshoot production problems to improve cheese quality. This approach can be extended using quantitative analysis, which enables further comparisons between structural features and functional measures used within industry, such as cheese meltability, shreddability, and stretchability, potentially allowing prediction and control of these properties. This review covers advances in the analysis of cheese microstructure, including new techniques, and outlines how these can be applied to understand and improve cheese manufacture.
We present the preparation and physicochemical properties of thermally induced emulsion gels of a soy protein isolate–whey protein isolate (SPI–WPI)/calcium chloride composite, and the analysis of their nutrient release behaviors using fat-soluble vitamin E as a model system by simulating its digestion in vitro. In general, the SPI–WPI composite emulsion gel was found to have better water-holding capacity and texture than the emulsion gels formed by the single protein. The microstructure and rheological properties of the gel suggested that the CaCl2 concentration significantly influences the fundamental structure and mechanical properties of the SPI–WPI gel. The in vitro digestion experiments revealed that the mixed protein emulsion gel improves the bioavailability of vitamin E. This study is of great significance in the utilization of these natural emulsifiers, as they can be used in the development of emulsion delivery systems for lipophilic nutrients and other health products.
Exploring facile and low-cost preparation route is desired for high-performance [email protected] ([email protected]) anode. Here, the amino acid units of protein molecules in egg white trap modified Si nanoparticles (NPs) through a facile ‘molecular cooking’ strategy, followed by incorporating the Si NPs into a functional carbon skeleton at nanoscale through in situ carbonization. The relationship between fundamental structure and properties is well studied. Experimental results reveal that the outer N-doped carbon layer can not only provide sufficient electrical conductivity for Li-ion reaction kinetics but can also enhances the stability of the interface between the active material and the Cu collector. The inner SiOx layer shows good lithium affinity, which can optimise the Li-ion transport path. The double layer can effectively buffer the huge internal strain of the Si core. The resultant hybrid [email protected]x@C composite with 32.4 wt% carbon content possessed superior rate capability (1062 mAh g⁻¹ at 6 A g⁻¹) and long-term stability (727 mAh g⁻¹ at 2 A g⁻¹ after 400 cycles). In addition, the fabricated full cell also demonstrated favourable Li-ion storage capability. This work provides a facile strategy for the preparation of other electrodes with serious continuous volumetric swelling–shrinking behaviour upon cycling.
The purpose of this study was to analyse the relationship between extracellular protease activity and gel characteristics of soybean protein gel induced by lactic acid bacteria (LAB), the influence of protease inhibition on the gel characteristics was discussed through SDS‐PAGE, rheological properties and microstructure. The results showed that the pH value of Lactobacillus casei decreased slowly, but the gel could be formed at 2 h, maybe its higher extracellular protease activity improved the gel characteristics. The addition of ethylenediaminetetraacetic acid (10 mmol L−1) reduced the gel quality, when the protease activity was inhibited, the gel quality would decrease, even if there were macromolecular crosslinkers in the system. This study showed that extracellular protease had an important influence on gel characteristics and provided a theoretical basis for the application of protease producing LAB in fermentation‐induced soybean gel foods. The effect of extracellular protease activity of lactic acid bacteria on gel hardness and water holding capacity were explored. The addition of protease inhibitors to inhibit protease activity caused the destruction of the gel network structure and the gel characteristics.
Almond proteins have potential utility in a range of food and beverages but it is not clear how pH affects protein structure and function. The behaviour of almond protein isolate was examined under conditions of neutral and acidic pH (pH 7 and 4). The isolate was highly soluble (70-80%) at either pH. An increase in acidity lead to protein unfolding, an increase in random coil structure and the appearance of lower molecular weight proteins due to acidic hydrolysis. These structural changes at pH 4 increased the capacity for foam formation and foam stability, increased viscosity and led to concentration and age dependent thickening. Gels, similar in strength but with distinct microstructures and properties were obtained following heating. At pH 7, a particulate type gel with an interconnected protein network was formed, while the gel at pH 4 had a dense continuous protein matrix. The gels differed in their susceptibility to chemical disruption, suggesting different underlying molecular interactions. The ability to alter protein structure and properties as a function of pH and heating could be used to broaden the application of almond proteins and develop a variety of food products, such as protein supplements and vegan alternatives to traditional products.
Oil, accounting for 45% of almonds, is easily oxidized and can further induce the protein oxidation to reduce their quality. Structure and physicochemical properties of amandin, the main water‐soluble protein in almonds, induced oxidation by malondialdehyde (MDA) were investigated. The results showed that the content of carbonyl group increased from 5.23 to 33.25 nmol/mg of protein with the increase of MDA concentration (p <0.05). However, the sulfhydryl content, surface hydrophobicity, particle size and the absolute value of ζ‐potential first increased and then decreased. Fourier transformed infrared spectroscopy (FT‐IR) confirmed that the structure of amandin changed from order to disorder. Fluorescence spectroscopic analysis revealed that mild oxidation (0‐0.1 mmol/L MDA) exposed hydrophobic groups of the protein. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) suggested that protein oxidation promoted cross‐linking between protein molecules. Furthermore, protein oxidation markedly declined the total amino acid content of amandin (p< 0.05). In conclusion, MDA oxidation changed the structure and amino acid content of amandin, and caused the protein aggregate and cross‐link through hydrophobic interaction and electrostatic interaction.
Meat analogue research and development focuses on the production of sustainable products that recreate conventional meat in its physical sensations (texture, appearance, taste, etc.) and nutritional aspects. Minced products, like burger patties and nuggets, muscle-type products, like chicken or steak-like cuts, and emulsion products, like Frankfurter and Mortadella type sausages, are the major categories of meat analogues. In this review, we discuss key ingredients for the production of these novel products, with special focus on protein sources, and underline the importance of ingredient functionality. Our observation is that structuring processes are optimized based on ingredients that were not originally designed for meat analogues applications. Therefore, mixing and blending different plant materials to obtain superior functionality is for now the common practice. We observed though that an alternative approach towards the use of ingredients such as flours, is gaining more interest. The emphasis, in this case, is on functionality towards use in meat analogues, rather than classical functionality such as purity and solubility. Another trend is the exploration of novel protein sources such as seaweed, algae and proteins produced via fermentation (cellular agriculture).
Wild almond (Amygdalus scoparia) is a drought-resistant, non-cultivated plant rich in protein. The extraction of protein isolates from wild almond was carried out using NaOH, buffered saline borate (BSB), and Tris–HCl and the isolates were characterized by their physico-chemical, thermal and emulsifying attributes. Use of BSB solution resulted in the maximum recovery of protein (56%, w/w) from wild almond. The amino acid compositions of wild almond protein isolates (WAPIs) were identified by high-performance liquid chromatography after acid hydrolysis. Aspartic and glutamic acids were the most abundant amino acids found in the WAPIs. Differential scanning calorimeter showed that WAPI is denatured above 80 °C. It was also found that the surface hydrophobicity values of the NaOH- and BSB-extracted proteins were 375 ± 6 and 359 ± 5, respectively. Water absorption capacities of isolates extracted by NaOH and BSB were 2.3 ± 0.4 and 2.6 ± 0.3 g water/g protein, respectively. In addition, oil absorption capacities for the isolates extracted using NaOH and BSB were 3.5 ± 0.7 and 3.1 ± 0.4 g oil/g protein, respectively. Moreover, the solubility levels of the extracted isolates increased up to 85.3% under alkaline conditions. The emulsion-activity indices of isolates increased at pH <4 and also at pH >4.5. In addition, the highest foaming capacity was obtained at pH 2 for the extracted isolates. In conclusion, the study has shown that WAPIs can enhance the oil absorption capacity, emulsifying and foaming properties. Thus, they could be considered for application as an ingredient for functional foods processed in alkaline conditions at temperatures below 80 °C.
Quality of plain set yoghurt was investigated by varying levels of ultrafiltration concentration of cow skim milk (1-without ultrafiltration, 1.5 and 2 folds) and inoculum (2, 2.5 and 3%) of yoghurt culture (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus 1:1). Titratable acidity development and pH reduction were significantly faster during incubation of yoghurt with increasing ultrafiltration concentration level and inoculum level. Increased ultrafiltration concentration level decreased spontaneous whey syneresis, but increased water holding capacity and firmness of the product significantly. Body & texture and overall acceptability scores were significantly better in yoghurts prepared from 1.5 fold concentrated milk irrespective of the inoculum level studied. Inoculum level did not show any significant effect on the quality of yoghurt, but higher inoculum level decreased the incubation period significantly. Optimized product was obtained with 1.5 fold concentrated skim milk standardized to 3.3% fat and incubated with 2% inoculum level in about five and a half hour of incubation. Optimized product had 13.60±0.02% total solids, 3.31±0.01% fat, 5.27±0.04% protein, 4.20±0.03% lactose and 0.82±0.02% ash. Whey syneresis, water holding capacity and firmness in optimized product were nil, 63.49% and 1.89 N, respectively. Thus, high quality plain yoghurt could be prepared by employing ultrafiltration, without addition of stabilizers, which is otherwise widely used commercially for the manufacture of yoghurt to control its wheying off and body.
Prunus dulcis, the cultivated sweet almond, has long been recognized as a source of nutrients in many traditional diets, and is increasingly promoted as a healthy snack and ingredient. This paper reviews the global research over the past 50 years that has contributed to knowledge on the composition and characterization of almond macronutrients and micronutrients, specifically the lipids and fatty acids, proteins and amino acids, carbohydrates (including dietary fiber), minerals and vitamins. Tables providing an overview of major macronutrient and micronutrient contents (range of means per 100g) as reported for almonds grown in various production regions are presented. Considerable variability in lipid content has been reported within and among commercial varieties and breeding selections; total lipids range from 25 to 66g/100g almonds (fresh weight). Oleic and linoleic acids account for about 90% of total lipids, and saturated fatty acid levels are very low (
Almond is one of the tree nuts listed by US FDA as a food allergen source. A food allergen identified with patient sera has been debated to be the 2S albumin or the 7S vicilin. However, neither of these proteins has been defined as a food allergen. The purpose of this study was to clone, express, and purify almond vicilin and test whether it is a food allergen. Western blot experiment was performed with 18 individual sera from patients with double-blind, placebo-controlled clinical almond allergy. The results showed that 44% of the sera contained IgE antibodies that recognized the recombinant almond vicilin, indicating that it is an almond allergen. Identifying this and additional almond allergens will facilitate the understanding of the allergenicity of seed proteins in tree nuts and their cross-reactivity
Three major protein components, namely, albumin, globulin, and glutenin, were extracted from Xinjiang SC‐1 defatted almond kernel powder using the Osborne classification method, and their molecular and structural properties were analyzed. SDS‐PAGE indicated that the molecular weight distribution of almond kernel proteins was within the range of 21–245 kDa. The percentages of essential amino acids in the defatted almond kernel powder, albumin, globulin, and glutenin were 31.17, 24.56, 32.22, and 39.96, respectively. Among the three major protein components, almond albumin had a relatively tighter and more stable structure, resulting in a higher denaturation temperature and lower surface hydrophobicity. Spectroscopic analysis demonstrated that the almond glutenin had more aromatic amino acids distributed on its surface and was more sensitive to ultraviolet and fluorescence spectrums. This information is essential for the understanding and application of almond kernel proteins.
Practical applications
The present study separated the defatted almond kernel powder into its major protein components, namely, albumin, globulin, and glutenin, and the structural properties of these three major protein components were analyzed. This study aimed to provide essential information for the research and application of the almond kernel proteins.
Due to the issues like lactose intolerance and milk allergy arising from the consumption of cow’s milk, there has been an increased demand in the plant based alternative milks around the world. Food industry has addressed these demands by introducing various milk beverages which are promoted as alternatives coming from plant sources which include almond milk and soy milk. Though they are popularly advertised as healthy and wholesome, little research has been done in understanding the nutritional implications of consuming these milk beverages in short term and long term. Further, consumers associate these alternatives to be a direct substitute of cow’s milk which might not be true in all cases. This review tries to address the issue by outlining the differences between cow’s milk and commercially available alternative milks in terms of their nutrient content. Though various plant based alternate milks have been studied, only the four most consumed milk beverages are presented in this review which are consumed widely around the world. A complete nutritional outline and the corresponding health benefits of consuming these plant based milk beverages have been discussed in detail which could help the consumers make an informed decision.
[Objective] The aim of this study is to investigate the physical and chemical properties of sweet almond albumin, globulin, gliadin and glutelin. The relationship between the change of protein's properties and product processing features was also studied to promote the development of high-quality sweet almond products. [Method] Alkali-solution and Acid-isolation was employed upon the skimmed sweet almond to extract crude protein, and, subsequently, Osborne classification method was adopted to extract the albumin, globulin, gliadin and glutelin. The amino acid composition was determined by Automatic Amino Acid Analyzer. ESEM was used to observe the morphological characteristics of above mentioned proteins; CD spectra scanning was utilized to measure its secondary structure; thermal properties were determined by using DSC and TGA; Rheometer was applied to determine the influence of shear rate, moreover, the linear equation between temperature and viscosity of proteins was determined, and, therefore, the value of Ea and K0 could be calculated. [Result] Various amino acids were detected in isolated proteins derived from sweet almond, containing 17 kinds of amino acids which the human need. It should be noticed that eight kinds of essential amino acids (including histidine) are completely embraced, among which the content of glutamic acid is the highest. Albumin, globulin and gliadin show a state of close aggregation structure, while glutelin shows a state of loose and porous plate. As for the constitution of the secondary structure, alpha helix and random curl are dominant in the isolated proteins compared with other forms of secondary structures. The denaturation temperatures for albumin, globulin, gliadin and glutelin are 62.84, 72.98, 78.33 and 45.70°C, respectively. Therefore, the thermal stability should coincide with the following order: gliadin > globulin > albumin > glutelin. Combined DSC with ESEM, the aggregation degree should conform to the following order: albumin > gliadin >globulin > glutelin protein. The aqueous solution of the four kinds of isolated proteins derived from sweet almond are non-Newtonian fluid and, furthermore, the relationship between temperature and viscosity is conform to the Arrhenius index equation, and the linear equation matches the parameters in processing well. [Conclusion] Sweet almond isolated protein can be regarded as a high-quality source for plant protein. Results of this study will make greater contributions to the development of sweet almond protein products. Besides, this study definitely do contribution to the function and property control of the protein products derived from sweet almond both in development and processing of the products, which could enhance the additional value and promote the development of sweet almond industry.
This work aimed to study the influence of pH (3.5 and 7.0) and CaCl2 and MgCl2 addition on heat-set gelation of a quinoa protein isolate at 10% and 15% (w/w). The protein isolate obtained was composed mainly of 11S globulin as was observed by electrophoresis and mass spectrometry analysis. Heat-set gelation occurred at both pH values studied. Nevertheless, the gels formed at pH 3.5 were more viscoelastic and denser than those formed at pH 7.0, that was coarser and presented syneresis. The CaCl2 and MgCl2 addition increased the gel strength during rheological analysis at pH 3.5, possibly due to the formation of fiber-like connections in the gel network. At pH 7.0, the divalent salts resulted in weaker gels formed by agglomerates, suggesting a neutralization of the protein surface charges. The differences in quinoa protein gelation were attributed to solubility, and the flexibility of proteins secondary structure at the pH studied.
Plant-based or non-dairy milk alternative is the fast growing segment in newer food product development category of functional and specialty beverage across the globe. Nowadays, cow milk allergy, lactose intolerance, calorie concern and prevalence of hypercholesterolemia, more preference to vegan diets has influenced consumers towards choosing cow milk alternatives. Plant-based milk alternatives are a rising trend, which can serve as an inexpensive alternate to poor economic group of developing countries and in places, where cow’s milk supply is insufficient. Though numerous types of innovative food beverages from plant sources are being exploited for cow milk alternative, many of these faces some/any type of technological issues; either related to processing or preservation. Majority of these milk alternatives lack nutritional balance when compared to bovine milk, however they contain functionally active components with health promoting properties which attracts health conscious consumers. In case of legume based milk alternatives, sensory acceptability is a major limiting factor for its wide popularity. New and advanced non-thermal processing technologies such as ultra high temperature treatment, ultra high pressure homogenization, pulsed electric field processing are being researched for tackling the problems related to increase of shelf life, emulsion stability, nutritional completeness and sensory acceptability of the final product. Concerted research efforts are required in coming years in functional beverages segment to prepare tailor-made newer products which are palatable as well as nutritionally adequate.
Background:
A study was conducted to investigate the impact of high pressure (450 and 600 MPa at 30 °C ) and thermal (72, 85 and 99 °C at 0.1 MPa) treatments on dispersive and aggregative characteristics of almond milk. Experiments were conducted using a kinetic pressure testing unit and water bath. Particle size distribution, microstructure, UV absorption spectra, pH and color changes of processed and unprocessed samples were analyzed.
Results:
Raw almond milk represented the mono model particle size distribution with average particle diameters of 2 to 3 µm. Thermal or pressure treatment of almond milk shifted the particle size distribution towards right and increased particle size by 5-6 fold. Micrographs confirmed that both the treatments increased particle size due to aggregation of macromolecules. Pressure treatment produced relatively more and larger aggregates than those produced by heat treated samples. The apparent aggregation rate constant for 450 MPa and 600 MPa processed samples were k450MPa ,30 (o) C = 0.0058 s(-1) and k600MPa , 30 (o) C = 0.0095 s(-1) respectively.
Conclusions:
This study showed that dispersive and aggregative properties of high pressure and heat treated almond milk are different due to differences in protein denaturation, particles coagulation and aggregates morphological characteristics. Knowledge gained from the study will help the food processors to formulate novel plant based beverages treated with high pressure.
The proximate analysis of almond seed and the physico-chemical characteristics of almond seed oil were found to be within the range of conventional oil seeds, except for a high protein content of 30.13%. The maximum extraction of solubilized and precipitated almond seed protein was found in the defatted sample at a 1:10 flour-solvent ratio using 0.03M NaOH and an extraction time of 20 minutes. Minimum and maximum nitrogen solubility index values were observed around pH 4 and 10, respectively. The protein concentrate had 4.25% moisture, 89.95% protein, 3.15% carbohydrate, 2.15% ash and no trace of fat. Water absorption, oil absorption, foaming, emulsion capacities and least gelation percentages were higher in the protein concentrate (220, 165, 69, 310 and 25%, respectively) than in the seed flour (198, 110, 38, 220 and 14, respectively). Almond seed was found to be a good source of calcium, potassium, magnesium, iron and phosphorous.
Solubility and stability properties of almond proteins were determined using ultracentrifugation and gel electrophoresis to gain a better insight into the complexity of these proteins. Ultracentrifugal analyses of the water-extractable proteins of defatted almond meal revealed four fractions of 2S, 9S, 14S and 19S. The 14S fraction corresponds to amandin, the classical globulin isolated earlier, and constitutes 65–70% of the extractable proteins. Variation of ionic strength from 0 to 1·0 at pH 6–8 showed no evidence of association–dissociation reactions that are typical of many oilseed and legume proteins. Polyacrylamide gel electrophoresis of the water-extractable proteins under reducing conditions separated two pairs of major polypeptides of 44 and 42 kDa and 27 and 25 kDa that appeared to be the respective acidic and basic polypeptides of amandin corresponding to the classical legumin model. Sodium chloride had no effect on total protein extractability but variation of extraction pH showed a broad minimum in extractability at pH 3–5. In contrast, when a pH 9 extract was lowered in pH, the minimum in protein solubility was narrower and shifted upward to pH 5 largely as a result of the precipitation of amandin. Interaction of amandin with phytate may explain the lower pH of minimum solubility when the meal was extracted directly as opposed to lowering the pH of an alkaline extract. Amandin is a cryoprotein and was obtained in 90% purity by cooling a water extract of defatted meal. Incubation of a water extract of meal in the presence of azide for about 12 days revealed proteolytic nicking of the acidic polypeptides of amandin apparently as a result of attack by endogenous proteinase(s). © 1998 Society of Chemical Industry.
The review summarizes some characteristics of the ultrastructure, contents, formation, and degradation of the protein bodies of plant seeds. Protein bodies bounded by a single membrane are common organelles for protein storage in plant seeds. They possess a homogeneous matrix in which crystalloids and/or globoids may be embedded. Apart from accumulated storage proteins several hydrolytic enzymes (proteases, phosphates), lectins, and inorganic ions, mainly as phytin (K-, Mg-, Ca-salt of myoinositol hexaphosphoric acid) are also present. Protein body formation within a distinct developmental stage of seed maturation involves the participation of other cellular compartments such as endoplasmic reticulum, vacuoles and probably dictyosomes. Storage protein breakdown during seed germination is accompanied by a fusion of protein bodies to larger vacuoles.
Cryo scanning electron microscopy (cryo SEM) and confocal laser scanning microscopy (CLSM) were used to visualise changes in the microstructure of milk, rennet-induced gel and curd during the manufacture of Cheddar cheese. Our results show that cryo preservation did not alter the microstructure of the sample when it was fixed by rapid freezing in slush liquid nitrogen due to the formation of amorphous ice. Artefacts such as the formation of ice crystals could be observed in samples when immersed directly into liquid nitrogen (−196 °C) at atmospheric pressure. These ice crystals changed the shape of sample pores increasing their size to >20 μm. The etching time, thickness of gold coating, accelerating voltage and type of detector used for cryo SEM observation were varied in order to minimise the formation of such artefacts and optimise conditions for imaging. Chains and clusters of casein micelles and fat globules were best observed in the gel and the cooked curd when the samples were freeze fractured and etched for 30 min, coated with a mixture of gold and palladium alloy approximately 6 nm thick at −140 °C and observed using a backscattered electron detector at 15 kV. The structure of the gel, curd and cheese was also observed using CLSM. Spherical fat globules were mostly present in the serum pores of the gel prepared from unhomogenised milk but were found embedded in the aggregated chains of the casein network within the gel prepared from homogenised milk when observed using CLSM. The porosity measurements obtained using cryo SEM were similar to those obtained using CLSM. These two complementary techniques can potentially be used to assist studies for the control of cheese texture and functionality.
The effects of pH (6.7 or 5.8), protein concentration and the heat treatment conditions (70 or 90 °C) on the physical properties
of heat-induced milk protein gels were studied using uniaxial compression, scanning electron microscopy, differential scanning
calorimetry, and water-holding capacity measurements. The systems were formed from whey protein isolate (10–15% w/v) with (5% w/v) or without the addition of caseinate. The reduction in pH from 6.7 to 5.8 increased the denaturation temperature of the
whey proteins, which directly affected the gel structure and mechanical properties. Due to this increase in the denaturation
temperature of the β-lactoglobulin and α-lactalbumin, a heat treatment of 70 °C/30 min did not provide sufficient protein
unfolding to form self-supporting gels. However, the presence of 5% (w/v) sodium caseinate decreased the whey protein thermo stability and was essential for the formation of self-supporting gels
at pH 6.7 with heat treatment at 70 °C/30 min. The gels formed at pH 6.7 showed a fine-stranded structure, with great rigidity
and deformability as compared to those formed at pH 5.8. The latter had a particulate structure and exuded water, which did
not occur with the gels formed at pH 6.7. The addition of sodium caseinate led to less porous networks with increased gel
deformability and strength but decreased water exudation. The same tendencies were observed with increasing whey protein concentration.
Unlabelled:
The effects of ultra-high-pressure homogenization (UHPH) at 200 and 300 MPa, in combination with different inlet temperatures (55, 65, and 75 °C) on almond beverages with lecithin (AML) and without lecithin (AM), were studied. UHPH-treated samples were compared with the base product (untreated), pasteurized (90 °C, 90 s), and ultra-high-temperature (UHT, 142 °C, 6 s) samples. Microbiological analysis, physical (dispersion stability, particle size distribution, and hydrophobicity), and chemical (hydroperoxide index) parameters of special relevance in almond beverages were studied. Microbiological results showed that pressure and inlet temperature combination had a significant impact on the lethal effect of UHPH treatment. While most UHPH treatments applied produced a higher quality of almond beverage than the pasteurized samples, the combination of 300 MPa and 65 and/or 75 °C corresponded to a maximum temperature after high pressure valve of 127.7 ± 9.7 and 129.3 ± 12.6 °C, respectively. This temperature acted during less than 0.7 s and produced no bacterial growth in almond beverages after incubation at 30 °C for 20 d. UHPH treatments of AML samples caused a significant decrease in particle size, resulting in a high physical stability of products compared to conventional heat treatments. UHPH treatment produced higher values of hydroperoxide index at day 1 of production than heat-treated almond beverage. Hydrophobicity increased in AML-UHPH-treated samples compared to AM and conventional treatments.
Practical application:
Ultra-high-pressure-homogenization (UHPH) is an emerging technology, a potential alternative to conventional heat treatments. It is a simple process consisting of single step. When liquid food (almond beverage in this study) passes through the high-pressure valve, a very good stability and reduction of microorganisms is achieved, both effects due to the particle breakdown. Specific UHPH conditions could produce commercial sterilization of almond beverage.
When hydrophobic parameters in addition to solubility were used, better correlations with protein functionality than using solubility alone were obtained. The hydrophobicity was measured fluorometrically before (S0) and after (Se) unfolding protein samples. Significant correlations were found for emulsifying capacity, emulsion stability, and fat binding capacity of heat-denatured proteins with surface hydrophobicity (S0) and solubility. For foaming capacity, an exposed hydrophobicity (Se) and viscosity played important roles; however, net charge was the most influential factor for foam stability. The Se and available SH-group content showed good correlations with thermal functional properties of proteins, e.g., heat coagulation, gelation, and thickening. Protein hydrophobicity, the hydrophile-lipophile balance (HLB) value of surfactants, and polarity of partition chromatography seem to be closely related. Ultimately, protein functionality is dependent on hydrophobic, electrostatic, and steric parameters of the proteins, which are all essential for defining the protein structure. More advanced data processing techniques, e.g., multivariate analysis, are needed for studying these relations.
The major U.S. marketing varieties of almonds contained moisture, protein, fat, and ash in the range 4.35–5.86%, 16.42–22.17%, 53.59–56.05%, and 2.69–2.93%, respectively. Two fatty acids, oleic (range 52.44–67.07%) and linoleic (range 22.05–38.67%) accounted for up to 90% of the total fat. The majority of almond proteins (≥ 95%) are water soluble with a minimum solubility at pH ≤ 4.0. Sodium chloride (1.0 M) decreased the almond protein solubility in aqueous medium. Electrophoretic analyses indicated that one water soluble protein dominates the almond protein composition. This oligomeric major protein is made up of two kinds of polypeptides (molecular weight range 20,000–22,000 and 38,000–41,000) linked via disulfide bonds. Among the proteases tested, pepsin was the most efficient in hydrolyzing the almond proteins.
Lipids in almonds are present as oil bodies in the nut. These oil bodies are surrounded by a membrane of proteins and phospholipids and are a delivery vehicle of energy in the form of triglycerides, similarly to the more studied bovine milk fat globule membrane. Chemical, physical and microscopic analyses revealed major differences in the composition and structure of almond oil bodies and bovine milk fat globules. The lipids of both natural emulsions differed in degree of unsaturation, chain length, and class. The almond oil body membrane does not contain any cholesterol or sphingomyelin unlike the bovine milk fat globule membrane. Therefore, the phospholipid distribution at the surface of the oil bodies did not present any liquid-ordered domains. The membranes, a monolayer around almond oil bodies and a trilayer around bovine fat globules, may affect the stability of the lipid droplets in a food matrix and the way the lipids are digested. (C) 2011 Elsevier Ltd. All rights reserved.
Almond protein isolate (API) formed a gel at 90 °C in 5 min at a concentration of 4% (w/v) in distilled deionized water adjusted to pH 8.2. The rate of API aggregation was dependent on the composition of the heating medium. Adding NaCl, NaBr, NaI, NaF, or NaSCN (each at 0.25, 0.5, 0.75, and 1 M) to the heating medium decreased the rate of thermal aggregation of API, while addition of 1 M CaCl2 promoted it. Hydrophobic interactions helped stabilize the API against thermal aggregation. Hydrogen bonds, ionic interactions, and disulfide exchange promoted the API thermal aggregation. Contribution of disulfide exchange to the API thermal aggregation was more than that made by the hydrogen and ionic bonds.
Almond ( Prunus dulcis ) has been widely used in all sorts of food products (bakery, pastry, snacks), mostly due to its pleasant flavor and health benefits. However, it is also classified as a potential allergenic seed known to be responsible for triggering several mild to life-threatening immune reactions in sensitized and allergic individuals. Presently, eight groups of allergenic proteins have been identified and characterized in almond, namely, PR-10 (Pru du 1), TLP (Pru du 2), prolamins (Pru du 2S albumin, Pru du 3), profilins (Pru du 4), 60sRP (Pru du 5), and cupin (Pru du 6, Pru du γ-conglutin), although only a few of them have been tested for reactivity with almond-allergic sera. To protect sensitized individuals, labeling regulations have been implemented for foods containing potential allergenic ingredients, impelling the development of adequate analytical methods. This work aims to present an updated and critical overview of the molecular characterization and clinical relevance of almond allergens, as well as review the main methodologies used to detect and quantitate food allergens with special emphasis on almond.
The particle size distribution of suspensions of fine particles was determined by a photocentrifuge from transmission/extinction profiles. Photocentrifuges provide a useful tool for the characterization and quality control of suspensions. While the variation of the light extinction curves caused by centrifugal segregation allows a qualitative description, a rigorous formulation provides a quantitative characterization. The present work reports on the determination of the particle size distribution using space and time resolved extinction profiles. The particle size distribution is obtained by analyzing the variation of the extinction at any point of the sample over the full centrifugation time or by analyzing the extinction variation over the entire sample length for any centrifugation time span. The advantage of the second method is the potential to save time.
Native, undenatured amandin and anacardein secondary structures were estimated to be, respectively, 56.4 and 49% β-sheet, 14 and 23.7% α-helix, and 29.6 and 27.4% random coil. Circular dichroic (CD) and fluorescence spectroscopy were used to assess structural changes in amandin and anacardein subjected to denaturing treatments that included heat (100 °C, 5 min), guanidium HCl (GuHCl), urea, sodium dodecyl sulfate (SDS), and reducing agent, 2% v/v β-mercaptoethanol (βME) + heat. Mouse monoclonal antibodies (mAbs) 4C10 and 4F10 directed against amandin and 1F5 and 4C3 directed against anacardein were used to assess the influence of denaturing treatments on the immunoreactivity of amandin and anacardein. Among the denaturing treatments investigated, SDS and β-ME caused a significant reduction in the immunoreactivity of amandin and anacardein when probed with mAb 4C10 and 4C3, respectively.
Borate saline buffer (0.1 M, pH 8.45) solubilized proteins from almond, Brazil nut, cashew nut, hazelnut, macadamia, pine nut, pistachio, Spanish peanut, Virginia peanut, and soybean seeds were prepared from the corresponding defatted flour. The yield was in the range from 10.6% (macadamia) to 27.4% (almond). The protein content, on a dry weight basis, of the lyophilized preparations ranged from 69.23% (pine nut) to 94.80% (soybean). Isolated proteins from Brazil nut had the lightest and hazelnut the darkest color. Isolated proteins exhibited good solubility in aqueous media. Foaming capacity (<40% overrun) and stability (<1 h) of the isolated proteins were poor to fair. Almond proteins had the highest viscosity among the tested proteins. Oil-holding capacity of the isolated proteins ranged from 2.8 (macadamia) to 7 (soybean) g of oil/g of protein. Least gelation concentrations (% w/v) for almond, Brazil nut, cashew, hazelnut, macadamia, pine nut, pistachio, Spanish peanut, Virginia peanut, and soybean were, respectively, 6, 8, 8, 12, 20, 12, 10, 14, 14, and 16.
Seed storage proteins are accumulated during seed development and act as a reserve of nutrition for seed germination and young sprout growth. Plant seeds play an important role in human nutrition by providing a relatively inexpensive source of protein. However, many plant foods contain allergenic proteins, and the number of people suffering from food allergies has increased rapidly in recent years. The 11S globulins are the most widespread seed storage proteins, present in monocotyledonous and dicotyledonous seeds as well as in gymnosperms (conifers) and other spermatophytes. This family of proteins accounts for a number of known major food allergens. They are of interest to both the public and industry due to food safety concerns. Because of the interests in the structural basis of the allergenicity of food allergens, we sought to determine the crystal structure of Pru1, the major component of the 11 S storage protein from almonds. The structure was refined to 2.4 A, and the R/Rfree for the final refined structure is 17.2/22.9. Pru1 is a hexamer made of two trimers. Most of the back-to-back trimer-trimer association was contributed by monomer-monomer interactions. An alpha helix (helix 6) at the C-terminal end of the acidic domain of one of the interacting monomers lies at the cleft of the two protomers. The residues in this helix correspond to a flexible region in the peanut allergen Ara h 3 that encompasses a previously defined linear IgE epitope.
Information relating to the resistance of food allergens to thermal and/or chemical denaturation is critical if a reduction in protein allergenicity is to be achieved through food-processing means. This study examined the changes in the secondary structure of an almond allergen, amandin, and its acidic and basic polypeptides as a result of thermal and chemical denaturation. Amandin ( approximately 370 kDa) was purified by cryoprecipitation followed by gel filtration chromatography and subjected to thermal (13-96 degrees C) and chemical (urea and dithiothreitol) treatments. Changes in the secondary structure of the protein were followed using circular dichroism spectroscopy. The secondary structure of the hexameric amandin did not undergo remarkable changes at temperatures up to 90 degrees C, although protein aggregation was observed. In the presence of a reducing agent, irreversible denaturation occurred with the following experimental values: T(m) = 72.53 degrees C (transition temperature), DeltaH = 87.40 kcal/mol (unfolding enthalpy), and C(p) = 2.48 kcal/(mol degrees C) (heat capacity). The concentration of urea needed to achieve 50% denaturation was 2.59 M, and the Gibbs free energy of chemical denaturation was calculated to be DeltaG = 3.82 kcal/mol. The basic and acidic polypeptides of amandin had lower thermal stabilities than the multimeric protein.
Using an improved method of gel electrophoresis, many hitherto unknown
proteins have been found in bacteriophage T4 and some of these have been
identified with specific gene products. Four major components of the
head are cleaved during the process of assembly, apparently after the
precursor proteins have assembled into some large intermediate
structure.
The influence of type of fluorescent probe on the surface hydrophobicity values determined for three native and heated proteins was assessed using uncharged [6-propionyl-2-(N, N-dimethylamino)naphthalene or PRODAN] versus anionic aliphatic (cis-parinaric acid or CPA) and aromatic (1-anilinonaphthalene-8-sulfonic acid or ANS) probes. Surface hydrophobicities of whey protein isolate, beta-lactoglobulin, and bovine serum albumin under heated (80 degrees C for 30 min) and unheated conditions and at varying pH values (3.0, 5.0, 7.0, and 9. 0) were measured using ANS, CPA, and PRODAN. ANS and CPA yielded opposing results for the effects of pH and heating on protein hydrophobicity. Hydrophobicity was lower at pH 3.0 than at other pH values for all proteins measured by PRODAN, whereas the values measured by ANS and CPA at pH 3.0 were quite high compared to those at other pH values, suggesting the influence of electrostatic interactions on anionic probe-protein binding. These results suggest that the presence or absence of a permanent charge as well as the aromatic and aliphatic nature of fluorescent probes can affect protein hydrophobicity values measured under various pH conditions.
Plant seeds store triacylglycerols (TAGs) in intracellular organelles called oil-bodies or oleosomes, which consist of oil droplets covered by a coat of phospholipids and proteins. During seed germination, the TAGs of oil-bodies hydrolysed by lipases sustain the growth of the seedlings. The mechanism whereby lipases gain access to their substrate in these organelles is largely unknown. One of the questions that arises is whether the protein/phospholipid coat of oil-bodies prevents the access of lipase to the oil core. We have investigated the susceptibility of almond oil-bodies to in vitro lipolysis by various purified lipases with a broad range of biochemical properties. We have found that all the enzymes assayed were capable of releasing on their own free fatty acids from the TAG of oil-bodies. Depending on the lipase, the specific activity measured on oil-bodies using the pH-stat technique was found to range from 18 to 38% of the specific activity measured on almond oil emulsified by gum arabic. Some of these lipases are known to have a dual lipase/phospholipase activity. However, no correlation was found to exist between the ability of a lipase to readily and efficiently hydrolyse the TAG content of oil-bodies and the presence of a phospholipase activity. Kinetic studies indicate that oil-bodies behave as a substrate as other proteolipid organelles such as milk fat globules. Finally we have shown that a purified water-soluble plant lipase on its own can easily hydrolyse oil-bodies in vitro. Our results suggest that the lipolysis of oil-bodies in seedlings might occur without any pre-hydrolysis of the protein coat.
Proteins and lipids, both individually or as complexes, play important functional roles in foods. Since the 1970s food scientists have devoted attention to the nature of these interactions and particularly to their effects on functional characteristics of protein-based foods. Previously, most of the published work was devoted to the biochemical aspects of protein-lipid interactions in biological systems. This article reviews the protein-lipid interactions of both naturally occurring protein-lipid complexes and protein-lipid complexes formed by induced interactions in foods and food products. The physicochemical characteristics of known protein-lipid complexes, the nature of binding which results in formation of these complexes and the effect of the interactions on food functionality are reviewed.
The almond major storage protein, amandin, was prepared by column chromatography (amandin-1), cryoprecipitation (amandin-2), and isoelectric precipitation (amandin-3) methods. Amandin is a legumin type protein characterized by a sedimentation value of 14S. Amandin is composed of two major types of polypeptides with estimated molecular weights of 42-46 and 20-22 kDa linked via disulfide bonds. Several additional minor polypeptides were also present in amandin. Amandin is a storage protein with an estimated molecular weight of 427,300 +/- 47,600 Da (n = 7) and a Stokes radius of 65.88 +/- 3.21 A (n = 7). Amandin is not a glycoprotein. Amandin-1, amandin-2, and amandin-3 are antigenically related and have similar biochemical properties. Amandin-3 is more negatively charged than either amandin-1 or amandin-2. Methionine is the first essential limiting amino acid in amandin followed by lysine and threonine.
Practically all foods contain particles. It has been suggested that the presence of particles in food may affect the perception of sensory attributes. In the present study we investigated the effect of size and type (hardness and shape) of particles added to a CMC based vanilla custard dessert. The two types of particles included in the study were silica dioxide and polystyrene spheres, varying in size from 2 to 230 μm. Eighteen trained adults participated in the study. They rated the sensation of 17 sensory flavour and texture attributes on a 100-point visual analogue scale (VAS). The results indicate that the addition of particles increased the sensation of roughness attributes and decreased the ratings of a number of presumably favorable texture attributes (smoothness, creamy, fatty and slippery) significantly. These effects increased with increasing particle size up to 80 μm. Roughness ratings deceased for larger particles sizes. Surprisingly, even particles of 2 μm had significant effects: they increased perceived rough lip–tooth feel, and decreased slippery lip–tooth feel and smoothness of the product. The affected attributes had previously been related to lubricative properties of foods. Particles added to semi-solid foods with relatively low levels of fat seem to counteract the lubricating effects of the fat resulting in increased oral friction.
Almond drinks and methods for their production
- D Callewaert
- G Festjens
- N Neirynck
Effect of high pressure homogenisation and heat treatment on physical properties and stability of almond and hazelnut milks
- Bernat