G.V.V. Liyanaarachchi’s research while affiliated with University of Colombo and other places

Study presents the variation in free amino acids (FAAs) and total AAs in rice at different milling degrees. Two rice cultivars; Pachchaperumal and Bg 406 were subjected to three (4%, 7%, 12%) degrees of milling, and the variations in AA composition of milled rice and resulting bran were studied. Milling caused significant ( p < .05) reduction (5.7%–40.0%) of AAs in rice. Milling accounted for an increase in density of FAAs with sweet and sour taste in rice while reducing FAAs with bitter taste. Parboiling unequivocally aided the retention of AAs in rice upon milling. A variety‐specific distribution of AAs was observed inside the rice grain. Despite the reduction in AAs upon milling, the nutrient density, which is the ratio between the essential to nonessential AAs was not reduced in rice . Rice bran contained nutritional gamma amino butyric acid (GABA) (19.6%–29.1%) and essential AAs (35.7%–38.8%). Novelty impact statement Milling is a post harvesting technique used in the production of rice that improves the physical properties of rice, which are desired by the consumers that include whiteness, translucency and sensory properties as well as the storage stability. The amino acid content in rice is significantly reduced with the increase in milling degree. However, milling increases the ratio between the sum of FAAs with sweet and sour taste to, sum of free amino acids with bitter taste, which could be attributed to one of the factors leading to the enhanced sensory quality observed with the well‐milled rice. Parboiling enables the retention of nutritionally and functionally important amino acids that include essential amino acids and gamma amino butyric acid (GABA) during the milling process.

Cooking accounted for significant (p<0.01) loss in free and total amino acids (AAs) in rice. Fully milled raw rice reported relatively the lowest loss in total AAs (TAAs) over majority of cooking techniques. Cooking rice with draining excess water, cooking after discarding the soaked water and cooking with higher water to rice ratios accounted for higher losses in AAs in all rice types. Cooking with rice cooker retained relatively more free AAs in rice. TAAs in raw rice types were not influenced by the cooking appliance while gas cooker accounted for significantly higher losses in TAAs in parboiled rice. Cooking rice with draining and after discarding the soaked water caused higher losses in nutritional gamma amino butyric acid (GABA). Change in AAs in different rice types significantly varied with the cooking technique used. Hence, the importance of cooking practices in ensuring the optimum AA retention in rice is highlighted.

With the aim of assessing the feasibility of utilization of amino acid (AA) profiles in characterization of rice varieties grown under distinct influential conditions, the impact of seasonal, geographical and varietal variations on AA and organic acid profiles in rice was investigated. Seven traditional rice varieties with diverse grain and agronomic characteristics were cultivated in two major distinct agro ecological regions of Sri Lanka across the two major cultivation seasons. The AA and organic acid compositions were determined using liquid chromatographic technique. Rice grains contained twenty AAs (41.2 - 75.1 mg/100 g) including Gamma Amino Butyric Acid (GABA) in free form and sixteen AA in bound form (70.0 - 105.4 g/kg). Rice grains contained low levels (4.3 - 103.3 mg/kg) of fumaric, succinic and malic acids while citric acid (314.6 - 534.5 mg/kg) being the major organic acid present. Wet agro-ecological conditions favored total AA formation in rice. The impact caused from the season was found pronounced over the impact arising from the geographical location on the AAs in free form in rice. Principal Component Analysis (PCA) indicated that AA profile could be used for differentiation of rice based on the season and the variety.

Parboiling imparts significant changes to nutritional composition of rice. The study presents the variations in amino acid (AA) composition of rice observed during parboiling process, observed in selected Sri Lankan rice cultivars. Upon parboiling, the change in levels of free and protein bound amino acids inconsistently varied across the rice cultivars and upon the parboiling technique. In comparison to non‐parboiled rice, parboiling resulted in pronounced increase in nutritional gamma amino butyric acid (GABA) levels ranging from 2 times up to 11 times rendering parboiled rice a functional food. Rice parboiled after soaking for 48 h using steam reported the highest free AA and GABA contents while, parboiling with steeping in boiling water after 24 h soaking accounted for higher TAA contents in rice. Hence, for production of parboiled rice with increased nutritive value in respect of AA levels, the significance of optimization of post processing conditions in parboiling is highlighted.

Investigation made on the variation in amino acid compositions among selected traditional and newly improved rice varieties cultivated in Sri Lanka is presented. The free amino acid (FAA) composition including gamma-amino butyric acid (GABA) and protein bound total amino acids (TAAs) of eleven traditional and seven improved rice cultivars grown at Batalagoda across the two major cultivating seasons in the country were evaluated. Significant variations (p < 0.05) in GABA levels, individual and total amino acids in free and protein bound form were observed among the studied varieties. Both traditional and improved varieties reported comparable mean total FAAs and TAA levels. However, significantly higher levels of GABA, which has health promoting functional properties, were found in newly improved rice varieties in comparison to the traditional varieties. Significant impact of seasonal variation on total amino acid levels was observed in majority of the varieties with most of the varieties reporting higher amino acid levels when cultivated during the “Maha”, which is the major cultivation season in the country. The Behethheenati rice out of the traditional, while Bg 300 rice out of the newly improved, was found the most beneficial among the investigated varieties. The potential significant contribution obtainable with several local traditional and improved varieties in fulfilling the majority of the recommended essential amino acid nutrient requirement in the daily diet by the world health organization is highlighted.

This study investigated the amino acid composition of eight local and three imported rice varieties frequently consumed by consumers in the capital of Sri Lanka. Investigation included twenty free amino acids (FAAs) analysed using liquid chromatography-tandem mass spectrometry (LCMS/MS) and sixteen protein bound amino acids analysed using high performance liquid chromatography with diode array detection (HPLC-DAD). The mean total amino acid (TAA) in rice ranged between 64.5 ± 1.9 g/kg and 96.0 ± 5.1 g/kg on dry basis (db). Ponni, Basmathi, Rathu Nadu and Fragrant rice which were parboiled varieties, reported the overall highest mean TAA contents while imported Ponni and Basmathi exhibited the highest mean essential amino acid (EAA) contents depicting high quality protein. Red rice varieties of Nadu, Kekulu and Kekulu Samba reported signifi cantly (p <0.05) higher mean TAA contents than their white counterpart varieties. The parboiled varieties; Rathu Nadu, Sudu Nadu, Keeri Samba and Samba reported the overall highest gamma amino butyric acid (GABA) contents (0.9 ± 0.3–5.0 ± 1.7mg/100g). Completely polished Sudu Kekulu reported the overall lowest mean TAA, EAA and GABA contents. Except for unanalysed tryptophan, fi ndings revealed that disregarding the nutritional loss encountered during cooking irrespective of variety, consumption of approximately 100 g of raw rice (after cooking) three times a day will provide an average adult (of 50 kg body weight) more than 50 % of the daily intake of essential individual amino acids recommended by the Food and Agricultural Organization (FAO).

The study presents the variation in free amino acids (FAAs) and total amino acid; (TAAs) in rice upon different degrees of milling. With the use of 0.2 g of the sample, amino acid levels in two rice cultivars resulting from three degrees of milling (DOM) (4%, 7%, well milled) and the resulting bran collected, each in three replicates were studied. FAA and TAA compositions varied significantly (p < 0.05) across the studied degrees of milling. For both cultivars, TAA content in the well refined rice, reduced to (70 ± 2) % of the TAA levels observed in the unmilled rice. Milling resulted in significant reduction in both total essential amino acid (TEAA) and total non essential amino acid (TNEAA) contents. Compared to unmilled rice, the levels of TEAA and TNEAA in highly refined white rice were reduced to t76.7 ± 2.3) % and (76.5 ± 0.8) % respectively. Further, the levels of non-proteinogenic amino acids which possess health promoting functional properties, garrma amino butyric acid (GABA), also decreased by (39.8 ± 5.6) % from the levels observed in unmilled rice. Moreover, the ratio between FAAs with sweet and sour taste to amino acids with bitter taste was significantly enhanced with increasing DOM and hence, could be one of the contributing factors for the increased consumer preference observed with well refined rice. In addition, significant variations in FAAs and relatively lesser variation in TAA distribution were observed in the bran collected from the various milling fractions, reflecting the distribution of FAA and TAA inside the rice granule. Therefore, the findings revealed that the nutritive value of rice is significantly reduced with increased DOM. Hence, from a nutritional perspective, the findings presented in this study provide an insight to the consumers and nutritionists in deciding food consumption patterns, and rice producers in revisiting their processing techniques.

Inspired by the apparent relationship of free amino acids (FAAs) which are present in minute quantities with the organoleptic characteristics of food, there is an increased demand for analytical methods sensitive in trace level detection. This study presents the validation results of a simple and rapid method developed for direct, underivatized analysis of FAAs in rice using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI). The method demonstrated satisfactory selectivity for twenty FAAs with minimum matrix effect. The recoveries obtained for samples fortified at three concentration levels: low mid and high, covering the working range of the method were in the range 80%-110%. The precision measured in terms of repeatability and reproducibility of the method expressed as percentage relative standard deviation (% RSD) were below 10% for the amino acids analyzed. The detection limits (LODs) and quantification limits (LOQs) of the method were in the range 0.4-1.0 mg/kg and 0.6-1.2 mg/kg respectively. Method had a wide linear range between 1.25-100 mg/kg with regression coefficients greater than 0.999 obtained over seven calibration levels. The method was also found robust over other cereals including corn, wheat and finger millet with satisfactory recoveries and precision values. The percentage expanded uncertainties calculated with the coverage factor of 2 (k = 2), were below 14% for the analyzed amino acids. The developed, simple and rapid LC-MS/MS method is accurate and reproducible, allowing determination of underivatized FAAs in rice and comply with the international method validation guideline requirements.