Saponin content of soya beans and some commercial soya bean products

Quantitative thin layer chromatography has been used to estimate the saponin content of whole soya beans (Glycine max L. Merrill, cv. Williams) and a number of commercial soya bean products such as protein isolates and lecithin. Saponins were present in all these materials at concentrations ranging from 56 g kg-¹ (on a dry weight basis) for whole soya beans to 3 g kg-¹ for the protein isolate ?Promine-D’?. Previous estimates indicate a saponin content of whole soya beans of only about 5 g kg-¹. It is suggested that this is an underestimate resulting from loss of material during the extraction procedures used in earlier methods of analysis.     

Saponin content of food plants and some prepared foods

Quantitative thin layer chromatography was used to estimate the saponin content of 20 common food plants and also of foods prepared from some of them. The food plants found to be richest in saponins were chickpeas (Cicer arietinum), soya beans (Glycine max), lucerne (alfalfa) sprouts (Medicago sativa) and varieties of Phaseolus vulgaris (navy beans, haricot beans, kidney beans). Saponins were not destroyed by processing or cooking. They were present in falafels (prepared from chickpeas), canned baked beans, canned broad beans and protein isolate from faba beans. However, the saponin content of a fermented soya bean product (tempe) was only half that of whole soya beans. Guar meal (Cyamopsis tetragonolobus) contains saponins but only a trace could be detected in samples of guar gum.     

Nutritional evaluation of meat–soya bean protein product blends

The nutritive value of protein of blends consisting of meat and soya bean protein products, which replaced either 20 or 40 % of protein of meat, were determined in rat feeding experiments. Protein efficiency ratio (PER) and net protein utilisation (NPU) were significantly lower (P<0.05) in blends containing either 20% protein from soya isolate or 40% protein from soya concentrate or soya flakes than blends containing sirloin only. However, there were no significant differences in PER and NPU when model meat (consisting of 70 and 30% protein from sirloin and connective tissue, respectively) was replaced by up to 20% protein from soya isolate or up to 40% protein from soya concentrate.     

Properties of soya milk and tofu prepared with γ-irradiated soya beans

Soya beans (Glycine max) ‘hwang keum’ were γ-irradiated at dose levels of 0, 2.5, 5, 10 and 20 kGy and the effects of the irradiated soya beans on soya milk and tofu properties were studied. An irradiation dose of 5 kGy caused an increase in yield of soya milk and tofu while having very little effect on their quality. The properties of tofu prepared with the soya beans irradiated at 2.5–5 kGy showed no significant difference from the non-irradiated control. However, at higher doses (10–20 kGy), decreases in yield, water holding capacity and sag value of tofu were observed. Compared with the non-irradiated control, hardness and fracturability in the texture of tofu were both significantly increased when the soya bean had been irradiated at 10–20 kGy, while cohesiveness and adhesiveness decreased. The changes in color values of soya milk and tofu were pronounced at 20 kGy.     

The determination of soya and meat protein in raw and processed meat products by specific peptide analysis. An evaluation

The detection and measurement of characteristic peptides formed on enzymatic hydrolysis of soya protein products, meats and offals is described. Samples were heated at 120°C for 3h prior to digestion with trypsin overnight, and the resultant peptide mixtures passed through an Amicon ultrafiltration membrane. After concentration the ultrafiltrates were analysed by ion exchange chromatography on Aminex A5 resin. Peptides were detected by post-column reaction with ninhydrin. Characteristic peaks designated SP 2 and MP 1 were seen in chromatograms of digests of soya protein isolate and beef respectively, and these peaks were well resolved in beef and soya protein isolate mixtures. The SP 2 peak was shown to contain peptides derived from soya 11 S globulin. The soya protein and beef contents of a series of mixtures of freeze-dried, defatted beef and soya protein isolate were determined by measurement of the SP 2 and MP 1 peaks respectively. Soya protein content could be determined within 2% of the true value over the range 30–70% soya protein isolate and beef content could be determined within 5% of the true value in the range 20–100% beef. Analysis of five soya protein isolates, four soya protein concentrates, six soya flours and 13 textured soya products indicated considerable interproduct variation in the yield of SP 2. The MP 1 peak was seen in a range of meats, both cooked and raw. It was also present in digests of offals which contained smooth or striated muscle but not in ‘non-muscle’ offals. The protein origin of the MP 1 peak was not established but the yield appeared lower in meat products which had been heated during manufacture than in those which had received no such treatment. Analysis of a series of laboratory prepared canned and heated pork and soya protein isolate mixtures enabled the pork content to be determined to within 8% of the true value, 2% soya protein isolate could be detected but not quantified accurately.     

The quantitative estimation of saponin in pea (Pisum sativum L.) and soya (Glycine max)

A thin-layer chromatographic method is described for the analysis of saponins in pea and soya flours. The results are compared with those of methods using gas chromatography and high performance liquid chromatography. The levels of saponin found in the air-classified fractions of pea flour are reported. The observed levels of saponin in soya, as estimated by thin-layer and gas chromatography (0·35% and 0·33%), are much lower than that previously reported using the former approach and reasons for this discrepancy are discussed.     

Selenium concentrations in soya based milks and infant formulae available in the United Kingdom

A simple hydride generation atomic absorption spectrometric method previously described for bovine infant formulae has been successfuly applied for the analysis of selenium in UK soya based milks and infant formulae. Levels reported for the first time ranged from 0.011 to 0.040 μg/g (wet wt) for soya milks and from 0.023 to 0.089 μg/g (dry wt) for soya isolate infant formulae. No matrix interferences were encountered and the mean recovery was 100.1%. These values exhibit variation between batches, hence routine QC analysis and fortification by manufacturers is recommended.     

Quantitative immunoassay for soya protein in raw and sterilized meat products

An enzyme-linked immunosorbent assay (ELISA) is described for the quantitative analysis of soya protein in meat products. The assay is applicable to raw and sterilized products and is not dependent on soya variety and type of soya ingredient (concentrate, isolate, etc.). Therefore, the assay can be applied without knowledge of product composition, heat pretreatment and other processing conditions. The ELISA is specific for soya; no interference of other product components has been found. The detection limit of the ELISA is 0.5% soya protein. Qualitative analysis by immunoblotting is possible at much lower concentrations. The antibodies used are specific for sodium dodecyl sulphate (SDS) denatured soya protein subunits. The products are extracted with SDS and 2-mercaptoethanol, which guarantees optimum recovery of the protein components. Product extracts can be analysed directly by ELISA without removal of the SDS by using nitrocellulose as a solid phase.     

复配型大豆浓缩蛋白功能特性的应用研究

主要介绍了一种复配型大豆浓缩蛋白在注射类肉制品中的应用。研究表明复配得到的浓缩蛋白应用于肉制品中时,不仅提高了肉制品的出品率,改善了肉制品的质构和口感,而且能够降低肉制品生产成本。感官评分显示,用注射复配型浓缩蛋白制作的肉制品在外观、风味、口感和总接受性等各项指标的评分均达到或高于添加注射型分离蛋白制作的产品。     

Quantitation of soya protein by enzyme linked immunosorbent assay of its characteristic peptide

An enzyme linked immunosorbent assay (ELISA) is described for the quantitative measurement of soya proteins in processed food products. The peptide fragment bearing an antigenicity against anti-glycinin (soya bean 11S globulin) antibody was purified from the trypsin digests of autoclaved glycinin and used as an indicator antigen for soya proteins. ELISA samples were prepared also by a combination of autoclaving and tryptic digestion. Quantitation of soya proteins by ELISA was found to resist interference by other food materials, and the ELISA signal was independent of soya bean cultivar. The ELISA method was evaluated on pork sausages which were prepared in the laboratory to contain 0 to 20·8% soya protein isolate. With commercial soya protein isolate as reference standard, the results showed that the detected amounts were in quantitative agreement with the added amounts of soya protein isolate.     

Effect of soya protein on the dialysability of exogenous iron and zinc

The investigation aimed at studying the influence of soya proteins on in vitro dialysability of exogenous iron and zinc. Soyabean was processed into various components like soya flour (SF), concentrate (SC) and isolate (SI) and two peptides (<30 kDa and >30 kDa). The protein contents of SF, SC and SI were 51, 62 and 78 g/100 g, respectively. Their iron contents ranged between 9.7 and 15.8 mg/100 g and zinc contents from 3.3 to 6.7 mg/100 g. Phytic acid contents (mg/100 g) of the soya components were SF 339, SC 226, SI 186 and peptides 18–20. In SF, percent dialysable iron and zinc were 12.6 and 50, respectively, this reduced to one-third and one-fifth in SC and SI. Dialysability of exogenously added minerals was found to be significantly lower in all soya protein components. However, the inhibitory effect was less pronounced in peptides. The protein component/matrix effect needs to be investigated to counteract the inhibitory effect of soya on iron dialysability.     

Trypsin inhibitory activity of raw soya bean after incubation with rumen fluid

Four soya bean (Glycine max Merr) inbreds, two of which (Williams 82 and Amsoy 71) capable of synthesising the Kunitz trypsin inhibitor (high trypsin inhibitory activity (TIA)) and two (L81–4590 and L83–4387), nearly isogenic to the former but lacking this particular function (low TIA) were used. In-vitro trials were performed to evaluate the residual TIA of flours incubated with runem fluid and the possible effect of proteinase inhibitors on rumen microbial fermentation, estimated by gas production. Only a slow fall in TIA was observed after short incubation times (5–10% at 2 h and 10–18% at 6 h), but after this period the rate of decline of TIA accelerated to give residual TIA of about 50% after 12 h and undetectable values after 48 h. Significant differences between genetic backgrounds were observed only at 2 h, when the Williams 82 background had a faster initial loss of TIA (89.1 versus 97.5% of the original activity, P < 0.01). Different patterns of TIA degradation were observed according to the presence/absence of the Kunitz inhibitor: inbreds lacking the Kunitz inhibitor initially had a higher residual TIA (95.9 versus 90.7%, P < 0.01) while at 12 and 24 h the residual TIA was considerably lower with respect to the other inbreds (45.4 versus 60.8 and 10.7 versus 20.4, respectively, P < 0.01). Gas production after 2 and 6 h of incubation was similar across treatments, whereas slightly but consistently more (P < 0.05) gas was produced at longer incubation times for inbreds lacking the Kunitz inhibitor. The results indicated that the proteinase inhibitors contained in raw soya bean are degraded at a much slower rate than previous nylon bag studies have suggested and that the presence of the Kunitz inhibitor leads to a higher residual TIA after rumen degradation and slightly lower microbial gas production.     

Preparation and characterisation of glyceollin‐enriched soya bean protein using solid‐state fermentation

Glyceollins, stress‐induced phytoalexins from parent soya bean isoflavones, were elicited with Aspergillus oryzae. This solid‐state fermentation facilitated the conversion of isoflavone glycosides into aglycones and glyceollins, which could mainly enrich in soya bean protein isolate (SPI) during protein preparation due to protein–polyphenol interactions. Glyceollin‐enriched SPI exhibited less flavour volatiles, higher solubility, lower whiteness and higher antioxidant activity than unfermented SPI. Fermented SPI was more easily to be digested during in vitro pepsin–trypsin digestion. This may be attributed to partial degradation of protein, especially α′ and α subunits of β‐conglycinin and acidic subunit of glycinin. The antioxidant activity of digestive products derived from fermented SPI was obviously enhanced with increasing digestion time due to simultaneous release of antioxidant peptides and glyceollins involved in the interior of protein molecule. These results suggest an effective technique for producing a nutrient‐enhanced SPI as novel functional ingredients applied in food industry.     

Role of carbohydrates in soya extrusion

When extruded under similar processing conditions, soya flour yielded a far more regular, honeycombed structure than soya isolate, though both had similar expansion ratios. At low concentrations both extrudates were almost totally soluble in solutions containing sodium dodecyl sulphate (SDS) plus 2-mercaptoethanol (ME), although in SDS or ME the extrudates were only partially soluble. These results suggest that, in both cases, the extrudates are primarily stabilized by disulphide bonds and hydrophobic interactions.
When rehydrated in water at temperatures in the range 20–120°C all the extrudates exhibited decreasing toughness and increasing protein solubility with increasing temperature. Also, the soya flour extrudates, but not those prepared from the isolate, exhibited a phenomenon at the lower temperatures characterized by minimum hydratability, pH and carbohydrate solubility at about 30–40°C. It is suggested that the soya flour extrudates are additionally stabilized, compared to the extrudates prepared from the isolate, by hydrophobic interactions involving the embedded carbohydrate.     

Chemical and Nutritional Studies on Mesquite Beans (Prosopis juliflora)

Mesquite beans (Prosopis juliflora) consisted of pericarp, hulls and kernels. With the exception of kernels, composition of beans and their fractions were protein, 10–15%; fat, 2–3%; crude fiber, 20–30%; sucrose, 21%; reducing sugars, 2–6%. Kernels contained 38% protein, 3% fat and 9% crude fiber. Bean trypsin inhibitor content was 1.4 TIU/mg. Bean protein isoelectric point was pH 5. Mesquite protein concentrate and isolate were prepared, however, by increasing solubility at the extraction pH (pH 10) with NaCl and decreasing it at the isoelectric point with (NH₄)₂SO₄. First and second limiting amino acids for bean protein were threonine and isoleucine, respectively; the protein was high in total sulfur amino acids and tryptophan. Corrected PER was 1.4.     

高效液相色谱法测定大豆发酵制品中的生物胺

目的从生物胺角度初步探讨大豆发酵制品的食用安全性,为确定大豆发酵制品的推荐安全摄入水平提供初步参考。方法采用柱前衍生高效液相色谱法检测大豆发酵制品中生物胺的含量,以0.4 mol/L高氯酸为提取液,以丹酰氯为衍生试剂,紫外检测波长254 nm。结果样品组分分离及测定结果重现性较好,豆豉、豆酱、酱油3种大豆发酵制品均有部分品牌组胺含量超过危害作用水平(即500 mg/kg),8个样品中有7种超过100 mg/kg,同类不同品牌大豆发酵制品间组胺含量没有明显差别;色胺均未检出;除组胺外,3种大豆发酵制品中尚可能存在2-苯乙胺、腐胺及尸胺。结论大豆发酵制品的色胺未检出,组胺含量较高,大量食用可能影响人体健康。     

Imitation milks from Cicer arietinum (L.), Vigna unguiculata (L.) walpers and Vigna radiata (L.) wilczek and other legumes

Vegetable milks were prepared in the laboratory from mung bean [Vigna radiata (L.) Wilczek], cowpea [Vigna unguiculata (L.) Walpers] and chick-pea [Cicer arietinum (L.)] by homogenisation of a filtered aqueous extract of the ground legume with soya bean oil. Emulsions stable to pasteurisation were made from the first two. Pigeon pea [Cajanus cajan (L.)] and black gram [Vigna mungo (L.) Hepper)] were found to be unsuitable as bases for milks prepared by simple processing. The nitrogen, oil, sugar and ash contents of the first three legumes, and of milks prepared from them, were determined. Imitation milks are intended to resemble animal milks nutritionally, and whilst the contents of potassium and phosphorus were acceptable, these vegetable milks were low in sodium, calcium and zinc. The trypsin inhibitory activity, whilst low in comparison with soya milk, was partially stable to pasteurisation. The amino acid composition indicated that it would be desirable to complement legume proteins with cereal proteins to prepare vegetable milks.     

Fate of oligosaccharides during production of soya bean tempe

The concentrations of the flatulence and possibly prebiotic oligosaccharides, stachyose and raffinose, as well as sucrose, glucose and fructose, were monitored during the preparation of bacteria‐free tempe made with Rhizopus oligosporus NRRL 2710. The initial soya beans contained (g [kg dry matter]⁻¹): stachyose, 30; raffinose, 11; sucrose, 57, glucose, <0.1, and fructose, <0.1. Losses of oligosaccharides during preparation of tempe were due to leaching during the hydration (100°C for 30 min), washing (60°C) and cooking stages (121°C for 10 min). The losses were (g [kg dry initial soya bean]⁻¹): hydration 45; dehulling and washing, 14, and cooking, 24. Concentrations remaining in the cooked cotyledons were (g [kg dry weight]⁻¹): stachyose, 7.0; raffinose, 2.1; sucrose, 7.2; glucose, 1.8, and fructose, 0.9, representing 17% (w/w) of the stachyose, 15% of the raffinose and 13% of the sucrose+glucose+fructose in the initial soya beans. Within the errors of measurement, concentrations of stachyose, raffinose and sucrose did not change during the fermentation but concentrations of glucose and fructose were reduced to 0.2 and 0.3 g (kg dry weight)⁻¹, respectively. The results are discussed in relation to controlling the concentrations of oligosaccharides in tempe. © 1999 Society of Chemical Industry     

In-vitro multienzyme digestibility of protein of some plant source flours blended with bovine plasma protein concentrate

The in-vitro multienzyme protein digestibilities of the flours of maize, cassava, pigeon pea (Cajanus cajan), African yambean (Sphenostylis stenocarpa) and bambara groundnut (Vigna subterranea), blended with bovine plasma protein concentrate were investigated. The multienzyme system consists of trypsin, chymotrypsin and peptidase. It was found that the addition of bovine plasma protein concentrate improved the protein digestibility of the flours compared with flours without the additive. The digestibilities were increased by between 3% in bambara groundnut blended flour to about 10% in cassava blended flour. When the flours were wet-heat treated, the digestibilities further increased in all samples with increments between 7·5 % in bambara groundnut and 16·6% in cassava flour. Bovine plasma protein concentrate may be a good source of protein for the fortification of protein-deficient foods, particularly maize and cassava flours.     

A simple, sensitive enzymatic method for quantitation of soya proteins in soya-meat blends

A method was developed for the detection and quantitation of soya proteins in soya-meat blends. The procedure involves acid hydrolysis of soya, meat or soya-meat blends and determination of free galactose plus arabinose using galactose dehydrogenase. Acetone powders of the various systems were also examined. Average galactose levels in soya flours, soya concentrates and soya isolates were 674,600 and 66 μM galactose equivalents per gram of product, respectively. Beef and pork contained less than 1 μM per gram of raw product. The galactose plus arabinose values for soya-meat blends were linearly dependent on the amount of soya added. The method is sensitive and capable of detecting less than 0·2% soya flours or concentrates and less than 2% soya isolates in meat products.