Pectin is extracted from dried lemon peel, after extraction of d-limonene. The remainder material is sold as excellent cattle feed with many benefi cial properties. (Adapted from Staunstrup 14 with kind permission.) 

Contexts in source publication

Context 1

... ‘pectic acid’ aft er the Greek word πηχτες ( pektes) for ‘coagulated material’, by Henri Braconnot in 1825, while continuing the studies of the gel-forming substance isolated from apple juice by Vauquelin in France in 1790, pectin is a heteropolysac- charide block co-polymer comprising 1,4-α-linked galacturonic acid and 1,2-linked rhamnose with side branches of either 1,4-linked β-D-galactose or 1,5-α-linked L-arabinose- ( Fig. 1). 1 In addition, some of the C-6 carboxyl units of the galacturonic acid backbone are esterifi ed with methoxyl groups, or exist as uronic acid salt. In general, the pectin polymer contains between 300 and up to around 1000 saccharide units (150 kDa molecular weight). Pectin is the main component of the primary walls of non-woody plant cells, and is abundant in most vegetables and fruit imparting strength and fl exibility to the cell wall, besides having a number of fundamental biological functions (signaling, cell proliferation, diff erentiation, and cell adhesion). 1 Th e rhamnose-rich regions of pectin chains enhance molecular interactions between cells and the polysaccharide, while the branched galactose-rich hairy regions promote the formation of entangled structures. 3 From a functional viewpoint, pectin is a hydrocolloid, namely a substance capable of trapping water and form- ing gels at low concentration. Being soluble in water and thanks to its excellent health and safety profi le, pectin is widely used for adding a desirable texture to food and beverages. In 2010, the European Food Safety Authority recognized the scientifi c validity of nutrition and health claims regarding pectin as a nutritional supplement in the reduction of post-prandial glycemic responses and the maintenance of normal blood cholesterol concentrations. It also increases satiety leading to a reduction in energy intake. 4 then discarded as waste – as valuable raw material in the production of a valued natural product. Today, pectin – mainly extracted from citrus peel – is a natural product of increasing importance knowing a con- stant growth in production and utilization. 5 Excellent books 1 and reviews detail the biochemistry 6 and the chemistry 7 of pectin, including thorough reviews on its pharmaceutical uses, 8 biomedical applications of pectin in various forms (polymer hydrogels, fi lms, tablets, microspheres, nanoparticles and scaff olds) as novel bioma- terial, 9 as well as on the emerging use of pectin-based edible fi lms incorporating natural antimicrobials for active food packaging. 10 Chemical and biochemical research on pectin actively continues worldwide. Suffi ce it to mention here the excep- tionally enhanced elasticity and mechanical strength of silk/pectin hydrogel, investigated as implantable bioscaf- fold material to regenerate cartilage and bone; 11 and the new method of treating chronic infl ammation by intravenous administration of aqueous modifi ed pectin solutions with molecular weights greater than 25 kilodaltons recently patented by a US pharmaceutical company. 12 We provide an updated overview of pectin extraction and applications in the context of the biorefi nery, namely the manufacturing unit of the emerging bioeconomy. 13 Th e study identifi es open opportunities toward larger scale production of this valued biopolymer, including eff orts toward broadening the sourcing of raw materials and improving the extraction methods. Off ering a unifi ed view of the main research and utilization trends, the study is concluded by arguments supporting our viewpoint that pectin will shortly emerge as a central product of the biorefi nery, and of the citrus-based biorefi nery in particular. Production of pectin started in Germany in the early 1900s when producers of apple juice started to cook dried apple pomace, the main by-product from the apple-juice manufacture. Th e extracted pectin was sold as a gelling agent. Demand was high, and in the 1930s the process was industrialized by new companies such as Opetka , Obipektin, and Herbstreith & Fox at new industrial sites established near apple-juice producers. Th e prolonged market success of this new product incidentally shows the industrial relevance of using a fruit by-product – until As already mentioned, today pectin is mostly produced from citrus peels and apple pomace, namely two by-products of fruit-juice production, with a minor fraction being obtained from sugarbeet (Fig. 2). Prior to pectin extraction with dilute mineral acids, the citrus peel must be dried from the starting level of about 82% moisture, down to 10–12% moisture so as to avoid fermentation. Because of the high water content and the perishable nature of the waste, drying is economically viable only if close to the processing (orange juice) plant, and only where large amounts of waste accumulate. In detail, aft er pressing the citrus fruit, the peel is dried at temperature that should not exceed 110°C. 15 Rotary or direct fi re dryers are normally used, avoiding direct con- tact between the fl ame and peel. Th e high cost of the desiccation plant and process per- haps explains why so few plants exist in southern Europe (where citrus is mostly grown), while Argentina leads the export of dried citrus peel to main citrus pectin manufacturers worldwide. Brazil and Mexico use orange and lime peel as the main pectin raw material (Fig. 3), while current production in China mainly relies on apple pomace. Independently of the raw material, however, the current manufacturing process is based on extraction via acid hydrolysis in hot water. Careful processing is needed with regard to both the pH and hydrolysis time, as polymeric degradation can otherwise rapidly take place. In detail, manufacturers use a dilute mineral acid (HCI or HNO 3 or H 2 SO 4 ) between 50°C and 100°C and at pH 2–3 for several hours to solubi- lize the protopectin. Following separation, the pectin extract is fi ltered, con- centrated, and precipitated with isopropyl alcohol. Th e alcohol is recovered by distillation while the pectin is washed and eventually dried. When pectin is extracted, much of the ‘hairy’ regions of the polymer are destroyed, leaving mainly the galacturonic acid ‘smooth’ regions, with a few neutral sugar units attached or in the main linear chain. Common yields of pectin are ~ 3% of the peel weight. 16 Eventually, out of a single lemon (200 g) aff ording the fi rst 100 g of wet peel and then 13 g of dry peel, typically 3 g of pectin is obtained, and 10 g of depectinized peel goes to cattle feed- ing (Fig. 3). Th e chemical characteristics of the extracted pectin depend on extraction conditions, and the sourcing material. Hence, prior to shipping, the product obtained is characterized (pectin for use in food is a polymer with at least 65% galacturonic acid units), and separated into low and high methoxyl pectin (LM and HM) with degree of esterifi cation (DE) >50% and <50%, respectively (Table 1). (Table 1). Th e DE value determines the degree of reactivity with calcium and other cations. Optionally, further de-esterifi cation of the high methylester pectin with acid or alkali, or amidation is carried out with ammonia to form amidated pectins which, when compared to LM pectins, need less calcium to gel, and are less sensitive to precipitation by high amounts of calcium. 17 Selected companies extracting pectin and commer- cializing it worldwide include CP Kelco (in Denmark and Brazil), Ceamsa (in Spain), Yantal Andre Pectin (in China), FMC Specialty Chemicals (USA), Du Pont Danisco (in the USA and Mexico), Herbstreith & Fox (in Germany), Naturex (production units in France, the USA, and Poland), Cargill Texturizing Solutions (in Belgium), Nexira (France) and Taiyo Kagaku (Japan), and B&V and Silvaextracts (in ...

Context 2

... ‘pectic acid’ aft er the Greek word πηχτες ( pektes) for ‘coagulated material’, by Henri Braconnot in 1825, while continuing the studies of the gel-forming substance isolated from apple juice by Vauquelin in France in 1790, pectin is a heteropolysac- charide block co-polymer comprising 1,4-α-linked galacturonic acid and 1,2-linked rhamnose with side branches of either 1,4-linked β-D-galactose or 1,5-α-linked L-arabinose- ( Fig. 1). 1 In addition, some of the C-6 carboxyl units of the galacturonic acid backbone are esterifi ed with methoxyl groups, or exist as uronic acid salt. In general, the pectin polymer contains between 300 and up to around 1000 saccharide units (150 kDa molecular weight). Pectin is the main component of the primary walls of non-woody plant cells, and is abundant in most vegetables and fruit imparting strength and fl exibility to the cell wall, besides having a number of fundamental biological functions (signaling, cell proliferation, diff erentiation, and cell adhesion). 1 Th e rhamnose-rich regions of pectin chains enhance molecular interactions between cells and the polysaccharide, while the branched galactose-rich hairy regions promote the formation of entangled structures. 3 From a functional viewpoint, pectin is a hydrocolloid, namely a substance capable of trapping water and form- ing gels at low concentration. Being soluble in water and thanks to its excellent health and safety profi le, pectin is widely used for adding a desirable texture to food and beverages. In 2010, the European Food Safety Authority recognized the scientifi c validity of nutrition and health claims regarding pectin as a nutritional supplement in the reduction of post-prandial glycemic responses and the maintenance of normal blood cholesterol concentrations. It also increases satiety leading to a reduction in energy intake. 4 then discarded as waste – as valuable raw material in the production of a valued natural product. Today, pectin – mainly extracted from citrus peel – is a natural product of increasing importance knowing a con- stant growth in production and utilization. 5 Excellent books 1 and reviews detail the biochemistry 6 and the chemistry 7 of pectin, including thorough reviews on its pharmaceutical uses, 8 biomedical applications of pectin in various forms (polymer hydrogels, fi lms, tablets, microspheres, nanoparticles and scaff olds) as novel bioma- terial, 9 as well as on the emerging use of pectin-based edible fi lms incorporating natural antimicrobials for active food packaging. 10 Chemical and biochemical research on pectin actively continues worldwide. Suffi ce it to mention here the excep- tionally enhanced elasticity and mechanical strength of silk/pectin hydrogel, investigated as implantable bioscaf- fold material to regenerate cartilage and bone; 11 and the new method of treating chronic infl ammation by intravenous administration of aqueous modifi ed pectin solutions with molecular weights greater than 25 kilodaltons recently patented by a US pharmaceutical company. 12 We provide an updated overview of pectin extraction and applications in the context of the biorefi nery, namely the manufacturing unit of the emerging bioeconomy. 13 Th e study identifi es open opportunities toward larger scale production of this valued biopolymer, including eff orts toward broadening the sourcing of raw materials and improving the extraction methods. Off ering a unifi ed view of the main research and utilization trends, the study is concluded by arguments supporting our viewpoint that pectin will shortly emerge as a central product of the biorefi nery, and of the citrus-based biorefi nery in particular. Production of pectin started in Germany in the early 1900s when producers of apple juice started to cook dried apple pomace, the main by-product from the apple-juice manufacture. Th e extracted pectin was sold as a gelling agent. Demand was high, and in the 1930s the process was industrialized by new companies such as Opetka , Obipektin, and Herbstreith & Fox at new industrial sites established near apple-juice producers. Th e prolonged market success of this new product incidentally shows the industrial relevance of using a fruit by-product – until As already mentioned, today pectin is mostly produced from citrus peels and apple pomace, namely two by-products of fruit-juice production, with a minor fraction being obtained from sugarbeet (Fig. 2). Prior to pectin extraction with dilute mineral acids, the citrus peel must be dried from the starting level of about 82% moisture, down to 10–12% moisture so as to avoid fermentation. Because of the high water content and the perishable nature of the waste, drying is economically viable only if close to the processing (orange juice) plant, and only where large amounts of waste accumulate. In detail, aft er pressing the citrus fruit, the peel is dried at temperature that should not exceed 110°C. 15 Rotary or direct fi re dryers are normally used, avoiding direct con- tact between the fl ame and peel. Th e high cost of the desiccation plant and process per- haps explains why so few plants exist in southern Europe (where citrus is mostly grown), while Argentina leads the export of dried citrus peel to main citrus pectin manufacturers worldwide. Brazil and Mexico use orange and lime peel as the main pectin raw material (Fig. 3), while current production in China mainly relies on apple pomace. Independently of the raw material, however, the current manufacturing process is based on extraction via acid hydrolysis in hot water. Careful processing is needed with regard to both the pH and hydrolysis time, as polymeric degradation can otherwise rapidly take place. In detail, manufacturers use a dilute mineral acid (HCI or HNO 3 or H 2 SO 4 ) between 50°C and 100°C and at pH 2–3 for several hours to solubi- lize the protopectin. Following separation, the pectin extract is fi ltered, con- centrated, and precipitated with isopropyl alcohol. Th e alcohol is recovered by distillation while the pectin is washed and eventually dried. When pectin is extracted, much of the ‘hairy’ regions of the polymer are destroyed, leaving mainly the galacturonic acid ‘smooth’ regions, with a few neutral sugar units attached or in the main linear chain. Common yields of pectin are ~ 3% of the peel weight. 16 Eventually, out of a single lemon (200 g) aff ording the fi rst 100 g of wet peel and then 13 g of dry peel, typically 3 g of pectin is obtained, and 10 g of depectinized peel goes to cattle feed- ing (Fig. 3). Th e chemical characteristics of the extracted pectin depend on extraction conditions, and the sourcing material. Hence, prior to shipping, the product obtained is characterized (pectin for use in food is a polymer with at least 65% galacturonic acid units), and separated into low and high methoxyl pectin (LM and HM) with degree of esterifi cation (DE) >50% and <50%, respectively (Table 1). (Table 1). Th e DE value determines the degree of reactivity with calcium and other cations. Optionally, further de-esterifi cation of the high methylester pectin with acid or alkali, or amidation is carried out with ammonia to form amidated pectins which, when compared to LM pectins, need less calcium to gel, and are less sensitive to precipitation by high amounts of calcium. 17 Selected companies extracting pectin and commer- cializing it worldwide include CP Kelco (in Denmark and Brazil), Ceamsa (in Spain), Yantal Andre Pectin (in China), FMC Specialty Chemicals (USA), Du Pont Danisco (in the USA and Mexico), Herbstreith & Fox (in Germany), Naturex (production units in France, the USA, and Poland), Cargill Texturizing Solutions (in Belgium), Nexira (France) and Taiyo Kagaku (Japan), and B&V and Silvaextracts (in ...