Particle size-starch–protein digestibility relationships in cowpea (Vigna unguiculata)

Physicochemical properties of flour produced from different cowpea (Vigna unguiculata) cultivars of Southern African origin

The variability and magnitude of interactions for food components and physicochemical properties of flour produced from five cultivars of cowpea (Glenda, Vegetable Cowpea 2, Vegetable Cowpea 3, Makathini, Embu Buff) were analysed using chemometrical techniques, for effective application as legume-based ingredients across different food product applications. Cowpea flour produced was defatted by extraction with n-hexane for 90 min (flour/solvent ratio of 1:3 w/v). Principle component analysis showed variation in chemical composition and physicochemical properties amongst cowpea flour studied. Flour produced are important sources of protein (24.30-26.33%), starch (50.99-51.33%), fiber (9.36-12.86%) and mineral elements. Pearson correlation analysis showed significant correlations amongst starch, mineral elements and physicochemical properties. Starch was found positively correlated with mineral elements sodium and calcium. Vegetable Cowpea 3 (50.55%) was found suitable for use in food products that are thawed for consumption. Mineral elements manganese, magnesium, phosphorous and sodium were found to significantly influence the pasting parameters (peak, trough, breakdown viscosity) studied. Understanding the magnitude of interactions between food components and physicochemical properties of cowpea flour would enable decisiveness over ingredient selection, improvement and management of quality for various legume-based food products. Furthermore, findings have the potential to assist in the development of improved cowpea cultivars.

Food matrix and processing modulate in vitro protein digestibility in soybeans

Soybeans represent the largest source of plant proteins on the planet but their proteins are associated with low digestibility. Although several studies addressed the limiting factors affecting the rate and extent of soy protein digestion, the net effect of the food matrix, especially of an intact cell wall, has been poorly investigated so far. The purpose of the present study was to examine the relationship between the cell matrix and protein hydrolysis during simulated in vitro digestion of soybean particles of different sizes prepared from unheated and boiled cotyledons. In addition, intact cells were isolated from unheated and autoclaved cotyledons and then digested with and without lipase inhibitors to understand the impact of an intact cell wall and the presence of oil bodies on soybean protein digestibility. Protein digestibility was the highest in the particles prepared after boiling of previously milled cotyledons compared to particles of the same size obtained by milling previously cooked cotyledons as well as of uncooked cotyledons. Protein digestibility in isolated intact cells was lower than that of extracted proteins regardless of the thermal load applied whereas inhibition of pancreatic lipase reduces protein digestibility only slightly. The data indicated that the cell wall could contribute to limit protein digestion in soybean tissues; however, it is not an absolute barrier to pancreatic proteases. An accurate design of the milling and cooking process could be instrumental to modulate the digestion kinetics of soybean proteins.

The microstructure of starchy food modulates its digestibility

Starch is the main carbohydrate in human nutrition and shows a range of desired food properties. It has been demonstrated that fast digestion of starchy food can induce many health issues (e.g., hyperglycaemia, diabetes, etc.); therefore, how to modulate its digestion is an interesting topic. Previous studies have revealed that the microstructure and digestibility of starchy food of different botanical origin or from multiple processes are quite different; modulating starch digestion by retaining or altering its microstructure may be effective. In the present review, the current knowledge of the relationship between microstructural changes to starchy food and its digestibility at molecular, cell and tissue, and food processing levels is summarized. New technologies focused on microstructure studies and ways to manipulate food microstructure to modulate starch digestibility are also reviewed. In particular, some insights focusing on the future study of microstructure and the digestibility of starchy food are also suggested.

Effects of ball milling treatment on physicochemical properties and digestibility of Pacific oyster (Crassostrea gigas) protein powder

The oyster protein was ball milling treated in this work, and the effects on particle size, conformation, physicochemical properties, and in vitro protein digestibility (IVPD) were investigated. After ball milling treatment, the particle size obviously decreased, and the protein powder became denser and more homogeneous. The ball milling treatment could not change the primary structure of oyster protein. However, it could affect the secondary structure and physicochemical properties. The disulfide bond increased from 8.18 to 9.14 μmol/g protein, while the protein surface hydrophobicity index increased from 0.088 to 0.176. The decreasing water-holding capacity from 390% to 226% and the increasing oil-binding capacity from 91.2% to 189.1% were related to the alterations of conformation and physicochemical properties. Ball milling could also improve the IVPD from 54.6% to 82.4%. These results provided theoretical basis for the application of ball milling treatment in the utilization of oyster protein in the food industry.

Research and regulatory gaps for the substantiation of protein content claims on foods

Protein claims provide guidance to consumers seeking protein-rich foods. Protein claim regulations differ globally, and both Canada and the United States require protein quality assessments. A tripartite workshop identified the need to (i) harmonize, (ii) update existing amino acid composition and digestibility databases, (iii) develop non-animal bioassays, and (iv) evaluate the impact of protein claims on human health. The Protein-Digestibility Corrected Amino Acid Score method is recommended for current regulatory use in Canada.

Effect of Processing on the In Vitro and In Vivo Protein Quality of Beans (Phaseolus vulgaris and Vicia Faba)

In this work, the protein quality of different bean types after undergoing the preparatory methods of baking, cooking and extrusion was assayed. Protein quality was assessed using a rodent bioassay to evaluate growth and protein digestibility while amino acid composition was determined via HPLC. In vivo protein digestibility was compared to an in vitro assessment method. The average protein digestibility corrected amino acid score (PDCAAS) for processed beans was higher than the digestible indispensable amino acid score (DIAAS) (61% vs. 45%). Extrusion/cooking of Phaseolus varieties resulted in higher PDCAAS (66% on average) and DIAAS values (61% on average) than baked (52% and 48%) while baked faba beans had higher PDCAAS (66%) and DIAAS (61%) values. A significant correlation was found between PDCAAS and in vitro PDCAAS (R² = 0.7497). This demonstrates which bean processing method will generate the optimal protein quality, which has benefits for both industrial production and individual domestic preparation.

Effect of tempering moisture and infrared heating temperature on the nutritional properties of desi chickpea and hull-less barley flours, and their blends

The impact of infrared heating surface temperature and tempering moisture on the nutritional properties of desi chickpea, hull-less barley, and their blends were examined. Specifically, this included changes to the level of anti-nutritive factors (i.e., trypsin/chymotrypsin inhibitors, total phenolics and condensed tannins), amino acid composition and in vitro protein digestibility. Results indicated that both temperature and the tempering/temperature treatment caused a reduction in levels of all anti-nutritional factors for both flours, and the effect was more prominent in the tempering-temperature combination. The amino acid composition of both flours was not substantially changed with tempering or infrared heating. The amino acid scores (AAS) of chickpea and barley flours, as determined by the first limiting amino acid using the FAO/WHO reference pattern found in the case of barley to be limiting in lysine with an AAS of ~0.9, whereas for chickpea flour, threonine was limiting and had an AAS of ~0.6. The in vitro protein digestibility of chickpea samples was found to increase from 76% to 79% with the tempering-heat (135 °C) combination, whereas barley flour increased from 72% to 79% when directly heated to 135 °C (without tempering). In vitro protein digestibility corrected amino acid score (IV-PDCAAS) was found to increase from 65% to 71% for chickpea flour and 44% to 52% for barley flour, respectively with tempering-temperature (135 °C) combination indicating that tempering with infrared heating can improve the nutritional value of both flours. The addition of chickpea flour to the barley flour acted to improve the nutritional properties (IV-PDCAAS), to an extent depending on the concentration of chickpea flour present.

Impact of Processing on the Protein Quality of Pinto Bean (Phaseolus vulgaris) and Buckwheat (Fagopyrum esculentum Moench) Flours and Blends, As Determined by in Vitro and in Vivo Methodologies

Blending of protein sources can increase protein quality by compensating for limiting amino acids present in individual sources, whereas processing grain flours by extrusion or baking can also alter protein quality. To determine the effect of baking and extrusion on the protein quality of blended flours from buckwheat and pinto beans, a rodent bioassay was performed and compared to an in vitro method of protein quality determination. Overall, extruded products had higher protein efficiency ratio values, increased digestibility, and greater protein digestibility corrected amino acid score (PDCAAS) values than baked products, with the extruded buckwheat/pinto blend having the greatest PDCAAS value of the experimental diets investigated. A correlation was found between both digestibility and PDCAAS values generated from in vitro and in vivo methods. The use of in vitro digestibility analysis should be investigated as a potential replacement for the current rodent assay for nutrient content claim purposes.

Heating Reduces Proso Millet Protein Digestibility via Formation of Hydrophobic Aggregates

Proso millet protein has reported structural similarities with sorghum. In order to explore the potential of this crop as an alternative protein source for people with gluten sensitivity, in vitro protein digestibility was analyzed. Dehulled proso millet flour was subjected to various processing techniques (dry heating and wet heating). Regardless of the processing technique there was a significant decline in digestibility of protein in proso millet flour when compared with unprocessed flour (from 79.7 ± 0.8% to 42.0 ± 1.2%). Reduced digestibility persisted even when cooking with reducing agents. Heating in the presence of urea (8 M) and guanidine-HCl (4.5 M) prevented the reduction in observed digestibility (urea cooked 77.4 ± 0.8%; guanidine HCl cooked 84.3 ± 0.9%), suggesting formation of hydrophobic aggregates during heating in water. This was supported by an increase in surface hydrophobicity upon cooking. Thus, the proso millet protein, termed panicin, forms hydrophobic aggregates that are resistant to digestion when subjected to heat.