Comparative impact of steaming and dry heat on functional components of soy hulls

Despite being a rich source of protein (28-34%), karanj (Pongamia glabra) cake is found to be bitter in taste and toxic in nature owing to the presence of flavonoid (karanjin), tannin and trypsin inhibitor, thereby restricting its safe inclusion in poultry rations.Feeding of karanj cake at higher levels (>10%) adversely affected the growth performance of poultry due to the presence of these toxic factors.Therefore, efforts were made to detoxify karanj cake by various physico-chemical methods such as dry heat, water washing, pressure cooking, alkali and acid treatments and microbiological treatment with Sacchraromyces cerevisiae (strain S-49).The level of residual karanjin in raw and variously processed cake was quantified by high performance liquid chromatography and tannin and trypsin inhibitor was quantified by titrametric and colorimetric methods, respectively.The karanjin, tannin and trypsin inhibitor levels in such solvent and expeller pressed karanj cake were 0.132, 3.766 and 6.550 and 0.324, 3.172 and 8.513%, respectively.Pressure-cooking of solvent extracted karanj cake (SKC) substantially reduced the karanjin content at a cake:water ratio of 1:0.5 with 30-minute cooking.Among chemical methods, 1.5% (w/w) NaOH was very effective in reducing the karanjin content.Ca (OH) 2 treatment was also equally effective in karanjin reduction, but at a higher concentration of 3.0% (w/w).A similar trend was noticed with respect to treatment of expeller pressed karanj cake (EKC).Pressure cooking of EKC was effective in reducing the karanjin level of the cake.Among chemical methods alkali treatment [2% (w/w) NaOH] substantially reduced the karanjin levels of the cake.Other methods such as water washing, dry heat, HCl, glacial acetic acid, urea-ammoniation, combined acid and alkali, and microbiological treatments marginally reduced the karanjin concentration of SKC and EKC.Treatment of both SKC and EKC with 1.5% and 2.0% NaOH (w/w) was the most effective method in reducing the tannin content.Among the various methods of detoxification, dry heat, pressure cooking and microbiological treatment with Saccharomyces cerevisiae were substantially effective in reducing the trypsin inhibitor activity in both SKC and EKC.Based on reduction in karanjin, in addition to tannin and trypsin inhibitor activity, detoxification of SKC with either 1.5% NaOH or 3% Ca (OH) 2 , w/w) and with 2% NaOH were more effective.Despite the effectiveness of pressure cooking in reducing the karanjin content, it could not be recommended for detoxification because of the practical difficulties in adopting the technology as well as for economic considerations.

The effect of various domestic processing methods on antinutrients and starch fractions and in vitro protein and starch digestibilities of white and black varieties of Mucuna pruriens var. utilis was studied. Cooking or autoclaving of both raw seeds and presoaked seeds in different solutions (water, tamarind extract, sodium bicarbonate, and citric acid) significantly (p < 0.05) reduced the content of total phenolics, phytic acid, trypsin inhibitor and chymotrypsin inhibitor activities, and L-dopa compared to soaking or dry heating techniques. The germination processes (24 and 48 h) were also effective in the reduction of various antinutrients, although this reduction appeared to be more pronounced in a prolonged period of germination (72 h). Water soaking followed by dehusking was found to be ineffective in the reduction of trypsin and chymotrypsin inhibitor activities in both varieties. All of the treatments were effective in significantly (p < 0.05) reducing the resistant starch content in the presently investigated samples. Cooking as well as autoclaving brought about a more significant (p < 0.05) improvement in the digestibility of protein and starch compared to germination and dry heat treatment. Moreover, among the different processing techniques, soaking in sodium bicarbonate solution followed by cooking (29.6-34.8%) or autoclaving (33.0-37.2%) seemed to be the best method for improving starch digestibility.

Soy foods contain significant health-promoting components but also may contain beany flavor and trypsin inhibitor activity (TIA), which can cause pancreatic disease if present at a high level. Thermal processing can inactivate TIA and lipoxygenase. Ultrahigh-temperature (UHT) processing is relatively new for manufacturing soy milk. Simultaneous elimination of TIA and soy odor by UHT processing for enhancing soy milk quality has not been reported. The objective was to determine TIA in soy milk processed by traditional, steam injection, blanching, and UHT methods and to compare the products with commercial soy milk products. Soybean was soaked and blanched at 70-85 degrees C for 30 s-7.5 min. The blanched beans were made into base soy milk. The hexanal content of the base soy milk was determined by gas chromatography to determine the best conditions for further thermal processing by indirect and direct UHT methods at 135-150 degrees C for 10-50 s using the Microthermics processor. Soy milk was also made from soaked soybeans by traditional batch cooking and steaming methods. Eighteen commercial products were selected from the supermarket. Residual TIA in soy milk processed by the traditional and steam injection to 100 degrees C for 20 min was approximately 13%. Blanching could inactivate 25-50% of TIAs of the raw soy milk. The blanch conditions of 80 degrees C and 2 min were selected for UHT processing because these conditions produced blanched soy milk without hexanal, indicating a complete heat inactivation of lipoxygenases. The TIA decreased with increased temperature and time of UHT heating. The maximal trypsin inhibitor inactivation was achieved by UHT direct and indirect methods with residual activities of approximately 10%. Some commercial soy milk products contained high TIAs. The results are important to the food industry and consumers. Kinetic analysis showed that heat inactivation (denaturation) of TIA, under the continuous processing conditions of the Microthermics processor, followed first-order reaction kinetics, and the activation energy of the inactivation was 34 kJ/mol.

Proximate composition, energy, mineral and vitamin contents and the effect of blanching methods and times on the trypsin and chymotrypsin inhibitor activities were studied using cabbage, collard, turnip, peanut, and sweet potato leaves. Results of this study indicated that, crude protein, crude fat, carbohydrate and ash contents were in the range of 15.5-25.6%, 1.4-6.5%, 60.4-73.1% and 6.8-7.5%, respectively. Total dietary fiber was lowest in cabbage (28.2 g/100 g) and highest in the collard leaves (43.1%) while energy content per 100 g of vegetables was highest in sweet potato leaves (402 kcal) and lowest in cabbage (379 kcal). The mineral content per 100 g of vegetables were in the range of 33.4-249.8 mg, 241.2-471.2 mg, 12.1-75.1 mg, 14.9-98.9 mg, 0.5-3.5 mg and 0.9-3.1 mg for Ca, K, Na, Mg, Fe and Zn, respectively. For ascorbic acid, riboflavin, thiamin and total carotenoids, concentrations in 100 g of vegetables were in the range of 45.1-112.7 mg, 0.2-0.3 mg, 0.3-0.8 mg and 2.0-7.3 mg, respectively. The trypsin inhibitory activity per gram of the vegetables was highest in collard (60.1 TIU/g) and lowest in peanut leaves (41.0 TIU/g). Chymotrypsin inhibitor activity was highest in the peanut (69.6 CIU/g) but lowest in the collard leaves (48.0 CIU/g). Both trypsin and chymotrypsin inhibitor activities were significantly (p < 0.05) reduced by most of the treatments in either the conventional or microwave blanching methods. In the conventional blanching method, trypsin inhibitor activity was reduced by 0.5, 6.8, 11.9, 9.0 and 19.3 percent in cabbage, collard, turnip, sweet potato and peanut leaves, respectively, when the vegetables were blanched for 2.5 minutes but after blanching for 10 minutes, the trypsin inhibitor activity was reduced by 29.7, 34.9, 54.3, 52.3 and 65.6 percent in cabbage, collard, turnip, sweet potato and peanut greens, respectively. For the microwave oven blanching, trypsin inhibitor activity was reduced by 3.8, 3.3, 32.7, 5.0 and 9.5 percent in cabbage, collard, turnip, sweet potato and peanut leaves, respectively when the vegetables were blanched for 30 seconds. When blanched for 60 seconds, trypsin inhibitor activity was reduced by 16.2, 45.8, 46.2, 51.0 and 42.4 percent in cabbage, collard, turnip, sweet potato and peanut greens, respectively. Similar trends in the reduction of chymotrypsin inhibitor activity were observed when the vegetables were conventionally blanched for 2.5, 5 and 10 minutes and when blanched by microwave oven for 30, 45 and 60 seconds. Based on the results of this study, the vegetables were good dietary sources of minerals, vitamins, carbohydrate and proteins. Also, blanching was an effective method for reducing the trypsin and chymotripsin inhibitor activities in the leafy vegetables, however, further investigation on the heating times for both conventional and microwave blanching methods is suggested.

Unheated and heated (121 degrees C, 66% moisture; 15, 30 and 45 min) Jatropha meals of non-toxic provenance from Veracruz state in Mexico were evaluated using rats and fish. With rats, the weight gain was highest for the casein diet followed by heated (30 min; only this treatment was studied using rats) and unheated Jatropha meal containing diets. The protein efficiency ratio (PER) for unheated and heated Jatropha meal containing diets was 37 and 86%, respectively, of the casein diet. On the other hand, the body weight gain, PER and feed conversion ratio of fish were statistically similar for unheated and heated (15, 30 and 45 min) Jatropha meal containing diets fed for a period of 35 days. Although these parameters were statistically similar for the unheated and heated Jatropha meal containing diets, the body weight gain, PER and protein productive value were highest and the feed conversion ratio lowest with 15 min heated Jatropha meal, suggesting that the heat treatment for 15 min is optimal for the meal. Trypsin inhibitor and lectin activities decreased drastically (>83 and 99%, respectively) after 30 and 45 min of heat treatment and after 15 min, the residual lectin activity was negligible and the residual trypsin inhibitor activity was 34%. These results, together with the nutritional parameters investigated, imply that Jatropha trypsin inhibitors and lectins do not have any adverse effects on carp at least up to 35 days of feeding. The nutritional value of Jatropha meal of the non-toxic provenance is high, and potential exists for its incorporation into the diets of monogastrics, fish and possibly humans.

Effect of processing on antinutrients and in vitro protein digestibility of the underutilized legume, Vigna unguiculata (L.) Walp subsp. unguiculata

Eighteen pea and five field bean varieties were analysed for trypsin inhibitor activity. Considerable variation was found between pea varieties, the values ranging from 0.15 to 4.62 TIU mg−1 under the assay conditions used. However, all the pea varieties, with the exception of Progretta and Maro, had a lower trypsin inhibitor content than the average value (1.49 TIU mg−1) obtained for the field bean varieties. The same varieties were also examined for chymotrypsin inhibitor activity and again considerable inter‐varietal variation was found. Chymotrypsin inhibitor activity was significantly higher for all the pea varieties, with the exception of the variety Minerva, than that found for the field bean varieties. Both trypsin and chymotrypsin inhibitor contents appeared to be independent of crude protein content and other seed characteristics, and in both species these protease inhibitors were largely unaffected by dry heat but were rapidly denatured by autoclaving. The significance of these results with respect to the potential of improving nutritive value by plant breeding are discussed.

Dry and moist heating-induced changes in protein molecular structure, protein subfraction, and nutrient profiles in soybeans

Enhancing the nutritional value of pea seed meals ( Pisum sativum) by thermal treatment or specific isogenic selection with comparison to soybean meal for African catfish, Clarias gariepinus

Pin milting and air classification of starchy legumes enriched the protein content of the light fraction to 49–75%, within the range of defatted soybean flours and protein concentrates. The levels of trypsin inhibitors, hemagglutinating activity, saponin, phytic acid and fiber were high in navy bean flour and the levels in the protein fractions of navy and northern beans greatly exceeded those of soybean flour. Potential nutritional problems in the air‐classified protein fractions of other legume species include trypsin inhibitor in lima bean and chickpea and saponin in lima bean, cowpea and lentil. Fababean and mung bean flours and protein fractions were comparatively lower in each antinutritive factor but fababean products contained vicine and convicine. SUMMARY THE EFFECTIVENESS of the pin milling and air classification of starchy legumes in the separation of protein and starch fractions has been amply demonstrated (Sosulski and Youngs, 1979). A previous study showed that the protein fractions also contained higher levels of oligosaccharides than the original flours while the starch fractions were depleted in sugars. In the present investigation, the concentrations of trypsin inhibitor, hemagglutinating activity and phytic acid in the protein fractions were up to 300% higher than the original flour while saponins and dietary fiber also tended to segregate with the protein. The starch fractions from most of the nine legume species and biotypes were substantially detoxified by the dry milling process. The protein fractions of navy and northern beans contained particularly high levels of essentially all of the antinutritive fractions and may require extensive processing if food uses of the products are anticipated. On the other hand, mung bean and fababean products were much lower than soybean flour in most antinutritive factors although the fababean protein fraction was enriched in vicine and convicine.

Variance analysis and variance components showed that total, heat-stable (HS) and heat-labile (HL) trypsin-inhibitor activity (TIA) of sweet potato [Ipomoea batatas (L.) Lam. 2n = 6x = 90] roots, expressed as units or specific units, were significantly different for monthly planting dates and cultivars. There were also significant differences among planting dates and cultivars for water-soluble (ws) protein content. Patterns of variation of total, HS, and HL TLA over 12 planting dates were similar and also similar to those of water-soluble protein content for four cultivars when TLA was expressed as units instead of specific units. When 12 values of TIA (units; total HS and HL) were plotted against water-soluble protein content, a positive correlation was found for all four cultivars. However, the positive correlation disappeared or weakened when TIA was evaluated as specific units. Stepwise removal of variables in multiple linear regression of cumulative rainfall, cumulative temperature, and TIA showed that there was a large negative correlation of the natural logarithm of TIA (units; total, HS and HL) on cumulative rainfall, suggesting that TIA may vary in response to drought of sweet potatoes.

In vitro rumen degradability of crude protein in seeds from four Sesbania spp. and the effects of treatments designed to reduce the levels of antinutrients in the seeds

Compounds in toasted soybean flour having trypsin inhibitor (TI) activity were isolated and characterized. Sodium hydroxide (0.01N) extracts of toasted soybean flour had an average of 2.59 mg TI/g sample. These extracts, after trichloroacetic acid (TCA) precipitation and dialysis, yielded supernatant and precipitate fractions. Addition of polyvinylpyrrolidone to eliminate free tannins and phenolics in the extracts, which may lead to overestimation of TI activity, was unnecessary. Material balance studies revealed 91% protein recovery and 92% recovery of TI activity in the TCA supernatant (1.1% protein, 2.0% TI) and precipitate (89.8% protein, 90.0% TI) fractions. Column chromatography and electrophoresis showed the TCA supernatant and precipitate fractions to contain proteins, including those having TI activity. Kunitz type TI and Bowman‐Birk type protease inhibitors accounted for most residual TI activity of toasted soybean flour, as verified by column chromatography, isoelectric focusing, sodium dodecyl sulfate polyacrylamide electrophoresis, and size‐exclusion high performance liquid chromatography, using the two similarly treated protease inhibitors as standards. Immunoblotting was also used to detect and identify Kunitz type TI’s in toasted soybean meal extracts. This study established the proteinaceous nature of residual trypsin inhibitor activity in toasted soybean flour and the presence of both Kunitz and Bowman‐Birk inhibitors.

Two ultrafiltered soy flour protein fractions were evaluated; the first was obtained by hydrolysis (0.5–3 kDa, F0.5–3), and the second was an enzymatically methionine-enriched fraction (1–10 kDa, F1–10E). Amino acid profiles, protein quality, allergenicity (against soy-sensitive infant sera) and trypsin inhibitor activity were determined. Fraction F1–10E fulfilled amino acid requirements for infants, whereas the F0.5–3 fraction was methionine deficient. Both fractions were similar in net protein utilization, and F1–10E digestibility was comparable with casein and higher (P < 0.05) than F0.5–3 or soy isolate. Allergenicity of SF was reduced to 21.5% with the hydrolysis in F1–10E and it was not detected in F0.5–3. Residual trypsin inhibitor activity with respect to soy flour was 8.1%, 3.3% and 1% for hydrolysate, F1–10E and F0.5–3, respectively. Both fractions presented high nutritive quality and reduced or null allergenicity. The trypsin inhibitor activity decreased along processing and could be a useful indicator for production of hypoallergenic proteins.

Modelling the Product Quality of Soybeans During Steaming