Protein quality, as determined by the PDCAAS method, is a measure of a protein's ability to provide adequate levels of essential amino acids for human needs. PDCAAS is calculated using an amino acid profile and true digestibility of a food protein. Soy protein is recognized as a high quality plant protein, but published PDCAAS values may vary based on the soy protein ingredient as well as the reproducibility and accuracy of the testing methods. Comparison of PDCAAS values for four differently processed soy ingredients, including three isolated soy proteins (ISP) and one soy protein concentrate (SPC), was made using two different laboratories with evaluation of the impact of the reproducibility and accuracy of amino acid profiles. PDCAAS calculations, using amino acid values from one laboratory, yielded a truncated PDCAAS of 1.00 for all four ingredients, while a second laboratory provided statistically significantly lower scores (0.95-1.00). We conclude that analytical method error can be a significant contributor to PDCAAS differences and can be mitigated by the application of amino acid nitrogen recovery correction factors.

Pea (Pisum sativum L. var. Laguna) seeds were submitted to extrusion process at 129, 135 and 142 °C and modifications on the proximate composition and nutritional parameters were evaluated. Peas were a good source of protein (24 g/100 g), amino acids (sulphur amino acids were the limiting ones), dietary fibre (18 g/100 g), carbohydrates (53 g/100 g), energy (330 kcal/100 g), riboflavin and thiamine (0.1-0.2 mg/100 g). Pea seeds also contained non-nutritive compounds such as α-galactosides (4 g/100 g), phytic acid (0.4 g/100 g) and trypsin inhibitor activity (2 TIU/mg). Extrusion cooking caused a slight increase of protein and fat content, whilst it reduced dietary fibre, thiamine and α-galactosides, and led to negligible trypsin inhibitor activity (TIA) levels. The protein quality of pea measured by biological indexes (net protein utilisation, net protein ratio, relative net protein ratio, true protein digestibility and biological value) was not affected by extrusion treatments. Protein quality measured by chemical indexes (chemical score and protein digestibility corrected amino acid score) decreased in processed peas. Among extruded peas, those processed at 135 °C presented the highest chemical indexes. Therefore, the aforementioned condition could be considered adequate for the manufacture of novel pea-derived products with high nutritive value. | This work has been funded by the Spanish Commission of Science and Technology AGL2010-16310 project, Buenos Aires University B426 project and Cereal and Oilseeds Centre of National Institute of Industrial Technology (INTI). | Peer Reviewed

A fração gérmen com pericarpo (farelo) é produzida no processamento do grão de milho, sendo usada para extração de óleo e alimentação animal. O estudo avaliou a qualidade nutricional e proteica desta fração em relação ao milho. Foi determinada a composição centesimal, conteúdo em minerais e perfil de aminoácidos da fração gérmen com pericarpo e do milho. Foi conduzido um experimento (4 semanas) com 36 ratos Wistar machos recém-desmamados, e foram formuladas três dietas contendo 10% de proteína (referência, gérmen com 15% de lipídios e caseína com 15% de lipídios), duas dietas com 6% de proteína (milho e caseína), e uma dieta aproteica. Foram constatados maiores teores de proteínas, lipídios, fibra alimentar (27,8 g.100g-1), cinzas, minerais (Fe e Zn - aproximadamente 5 mg. 100g-1) e lisina (57,2 mg.g-1 proteína) no gérmen em relação ao milho. O gérmen apresentou proteína de boa qualidade (Relative Protein Efficiency Ratio-RPER = 80%; Protein Digestibility-Corrected Amino Acid Score-PDCAAS = 86%), superior à do milho (RPER = 49%; PDCAAS = 60%). A fração gérmen com pericarpo é rica em fibra alimentar e é fonte de proteína de boa qualidade e de ferro e zinco, sendo indicado seu uso como matéria-prima nutritiva em produtos alimentícios para consumo humano. | The germ fraction with pericarp (bran) is generated in the industrial processing of corn kernel, and it is used for oil extraction and animal feed. This study evaluated the nutritional and protein quality of this fraction in relation to whole corn. The proximate composition, mineral contents, and amino acid profile of the germ fraction with pericarp and of whole corn were determined. A 4-week experiment was conducted using 36 weanling male Wistar rats, and three 10%-protein diets (reference, germ with 15% lipids and casein with 15% lipids), two 6%-protein diets (whole corn and casein), and a protein-free diet were prepared. The germ showed higher contents of proteins, lipids, dietary fiber (27.8 g.100 g-1), ash, minerals (Fe and Zn- approximately 5 mg.100 g-1), and lysine (57.2 mg.g-1 protein) than those of corn. The germ presented good quality protein (Relative Protein Efficiency Ratio-RPER = 80%; Protein Digestibility-Corrected Amino Acid Score-PDCAAS = 86%), higher than that of corn (RPER = 49%; PDCAAS = 60%). The corn germ fraction with pericarp is rich in dietary fiber, and it is a source of good quality protein as well as of iron and zinc, and its use as nutritive raw material is indicated in food products for human consumption.

Kisra is a naturally lactic acid bacteria- and yeast-fermented sorghum thin pancake-like flatbread produced in Sudan. Kisra has considerable potential as the basis for development of a gluten-free sandwich wrap. To help direct cultivar selection for commercial production of these products, two white, tan plant non-tannin Type I, one white Type II tannin, and one red Type III tannin sorghum cultivars were evaluated with respect to kisra protein quality and physical characteristics. Kisra from the non-tannin sorghums were flexible and had an open-textured structure with many regular gas cells, whereas those from the tannin sorghums were more brittle, denser in structure, and contained far fewer and smaller gas cells. Kisra from the tannin sorghums had the lowest reactive lysine content, in vitro protein digestibility, and Protein Digestibility Corrected Amino Score (PDCAAS), with values being lowest for the Type III sorghum. PDCAAS of kisra from the Type III sorghum was only 0.12, less than half of that from the Type I sorghums. As the tannins in tannin sorghums adversely affect kisra protein quality and physical characteristics, white tan plant, non-tannin sorghum cultivars are most suitable for kisra production and for development of wrap-type sorghum-based baked goods.

Kisra is a naturally lactic acid bacteria- and yeast-fermented sorghum thin pancake-like flatbread produced in Sudan. Kisra has considerable potential as the basis for development of a gluten-free sandwich wrap. To help direct cultivar selection for commercial production of these products, two white, tan plant non-tannin Type I, one white Type II tannin, and one red Type III tannin sorghum cultivars were evaluated with respect to kisra protein quality and physical characteristics. Kisra from the non-tannin sorghums were flexible and had an open-textured structure with many regular gas cells, whereas those from the tannin sorghums were more brittle, denser in structure, and contained far fewer and smaller gas cells. Kisra from the tannin sorghums had the lowest reactive lysine content, in vitro protein digestibility, and Protein Digestibility Corrected Amino Score (PDCAAS), with values being lowest for the Type III sorghum. PDCAAS of kisra from the Type III sorghum was only 0.12, less than half of that from the Type I sorghums. As the tannins in tannin sorghums adversely affect kisra protein quality and physical characteristics, white tan plant, non-tannin sorghum cultivars are most suitable for kisra production and for development of wrap-type sorghum-based baked goods.

Protein malnutrition is a problem in Africa where sorghum is a staple foodstuff. Improvement in the protein quality of traditional African sorghum (Sorghum bicolor L. Moench) foods through the addition of cowpea (Vigna unguiculata L. Walp), an indigenous African legume, was investigated. Two sorghum cultivars, a red, tannin-type (NS 5511) and a white tan-plant, non-tannin type (Orbit) were complemented with cowpea (70:30 ratio). Ugali (thick porridge), uji (fermented thin porridge) and injera (fermented flatbread) were prepared. The protein lysine scores of cowpea-complemented foods were about double the levels of sorghum-only foods. The in vitro protein digestibility of the foods increased by 13–62%. The increase in lysine and protein digestibility improvement resulted in three- and two-fold improvement in the Protein Digestibility Corrected Amino Acid Score (PDCAAS) of NS 5511, and Orbit foods, respectively. Addition of cowpea to tannin, as well as non-tannin sorghum is a viable option for improving the protein quality of a wide range of traditional African foods.

Eri silkworm (Samia ricinii) is a traditional source of food in northeast India, where it is grown primarily for silk and food uses. Nutrient analysis showed that the proximate composition of eri silkworm prepupae and pupae grown on either castor or tapioca were comparable and it was a good source of protein (16g%), fat (8g%) and minerals. The amino acid scores of eri prepupae and pupae protein were 99 and 100, respectively, with leucine as the limiting amino acid in both cases. Net protein utilisation (NPU) of prepupae and pupae was 41 as compared to 62 in casein. Protein digestibility corrected amino acid score (PDCAAS) was 86. The high protein content in the defatted eri silkworm meal (75%) with 44% total essential amino acids makes it an ideal candidate for preparing protein concentrate isolates with enhanced protein quality that can be used in animal nutrition.

This introductory review gives an overview on protein metabolism, and discusses protein quality, sources, and requirements as well as the results from recent studies on Swiss spontaneous protein consumption. To assess protein quality in protein mixes and foods, the ”protein digestibility-corrected amino acid score” (PDCAAS) is presented as a valuable tool in addition to the biological value (BV). Considering protein intake recommendations, the lower limit recommended has been defined according to the minimal amount needed to maintain short-term nitrogen balance in healthy people with moderate activity. Evaluation of intakes in Switzerland from food consumption data is about 90 g/day of protein per person. Two-thirds of proteins consumed in Switzerland are animal proteins with high biological value [meat and meat products (28 %), milk and dairy products (28 %), fish (3 %), and eggs (3 %)] and about 1/3 of proteins are of plant origin (25 % of cereals, 3 - 4 % of vegetables). Actual spontaneous protein consumption in Switzerland by specific groups of subjects is well within the actual recommendations (10 - 20 % of energy) with only the frail elderly being at risk of not covering their requirements for protein.

Protein Energy Malnutrition (PEM) due to under nutrition is a major public health problem among children in Africa and other developing countries. Sorghum and bread wheat, which are important dietary staples in the semi-arid tropics of Africa, are suitable vehicles for delivering proteins to alleviate PEM. Formulation of foods from these low-lysine staples fortified with legumes is a sustainable approach to improve the protein nutritional quality of foods for young children. Biscuits offer a valuable vehicle for fortification as they are nutrient dense, ready-to-eat, have a long shelf-life and are popular. Therefore, this study investigated the effect of complementing sorghum and bread wheat with defatted soy flour on the nutritional and sensory quality and consumer acceptability of biscuits. Biscuits were formulated and developed by compositing sorghum and bread wheat flours with defatted soy flour at different ratios. To establish the nutritional characteristics of biscuits, proximate composition, lysine and reactive lysine contents and in vitro protein digestibility were determined. Protein Efficiency Ratio (PER), Food Efficiency Ratio (FER) True Digestibility and Biological Value (BV) of sorghum biscuits were determined using Sprague Dowley weanling male rats. The sensory characteristics of biscuits were evaluated using a descriptive panel and instrumental texture analysis. Acceptability was evaluated using eight to nine year old school children. Compared to the 100% cereal biscuits, sorghum-soy and bread wheat-soy composite biscuits in a 1:1 ratio had at least double the protein, mineral and crude fibre contents. The lysine contents of biscuits increased by 500-700%. For the sorghum-soy biscuits, in vitro protein digestibility increased by 170% and Protein Digestibility Corrected Amino Acid Score (PDCAAS) was 8 times higher. Two such biscuits of 28 g each could provide 50% of the recommended daily protein intake for 3 to 10 year olds. In the animal study, PER and FER for sorghum-soy biscuits were equivalent to the reference casein. True Digestibility was high for all diets, 85 to 95% and BV of sorghum biscuits was higher than sorghum-soy diet by 20%. Principal Component Analysis (PCA) revealed that 61% and a further 33% of the variation in sensory properties was due to the type of cereal and concentration of soy in biscuits, respectively. Maximum stress increased by 39% and 34% in sorghum-soy and bread wheat-soy biscuits, respectively at 1:1 ratio. Spread factor of biscuits increased by 7 to 32%. Biscuits were darker in colour (reduced L* value) by 14 to 56% and hardness increased by 84% in sorghum biscuits. Positive hedonic scores by 8 to 9 year old school children for fortified biscuits were sustained above 80% through 8 consumption occasions. This data shows that fortifying with defatted soy flour imparts positive sensory characteristics associated with biscuits to sorghum and bread wheat biscuits and the acceptance of such biscuits may be sustained over an extended period of time. This study indicates that soy fortified sorghum and bread wheat biscuits have high nutrient density, protein quality, positive sensory properties and high acceptability if consumed over an extended period. Hence, the biscuits have great potential as protein-rich supplementary foods to alleviate PEM among children and to provide an income to small holder farmers in rural African communities through purchase of grain for the Home Grown School Feeding Programme.