Aggregation profile, preparation and nutritional characterization of African yam bean (Sphenostylis stenocarpa) acid and salt protein isolates

Aggregation tendencies of African yam bean (Sphenostylis stenocarpa) protein in the various aqueous extraction media with Ca²⁺, Mg²⁺ or at pI (isoelectric point) were determined. Water extractable S. stenocarpa protein aggregates more with addition of either Ca²⁺ or Mg²⁺ than at pI. In alkaline extractants considered (except at pH 10), aggregation tendency of the protein is in the order: pI > Ca²⁺ > Mg²⁺. The protein aggregation trend in salt media is a function of the salt type, aggregation in NaCl solution is of order: Ca²⁺ = pI > Mg²⁺, while in Na₂SO₄, we had pI > Mg²⁺ > Ca²⁺. S. stenocarpa protein aggregation was significantly (P < 0.05) more in Na₂SO₄ than NaCl. The amount of Ca²⁺ required for maximum precipitation of S. stenocarpa from alkaline (water-pH10) extractant was higher than that of Na₂SO₄ and more Ca-proteinate was obtained from the alkaline aliquot. The crude protein of the Ca-proteinates and isoelectric protein isolates obtained from salt and alkaline extract were in the range 71.7–91.8% (dry basis). Protein isolate from alkaline extract had significantly (P < 0.05) higher fat content than the one from salt extract. Isoelectrically precipitated isolates had lower ash content than Ca-proteinates. The percentage ratio of essential to non-essential amino acid was in the range 45–47%. With reference to FAO/WHO standard, the chemical score showed that most of the essential amino acid were in excess, thus, the amino acid distribution of S. stenocarpa protein isolates showed that it can fulfill the essential amino acid requirement of human especially the acid proteins and can be a good protein supplement in food and a wide range of new food products.     

Rheological properties of African yam bean (Sphenostylis stenocarpa Hochst. Ex A. Rich.) calcium proteinate and isoelectric protein isolates

The rheological characterizations of African yam bean (Sphenostylis stenocarpa) protein dispersions were investigated. Isoelectrically precipitated protein-IP_alk and IP_salt isolates obtained from alkaline and salt extractions respectively were more soluble than calcium precipitated proteins (CaP_alk and CaP_salt) at pH 3, 7 and 8. Regression analysis showed that Power law, Casson and Bingham rheological models adequately described rheological behaviors of S. stenocarpa protein dispersion. However, Power law gave the best fit. The flow behavior indices (n), at different ionic strength, pH, and temperature media were less than unity, indicating that S. stenocarpa protein dispersion exhibited pseudoplastic behaviors under the conditions tested. Salt extracted proteins were more pseudoplastic than alkali extracted counterpart with n for salt extracted proteins (IP_salt & CaP_salt) lower than that of alkali extracted protein (CaP_alk & CaP_salt). This is a numerical indication that salt extracted S. stenocarpa proteins were of larger shear-thinning tendency than the alkali extracted proteins. The consistency coefficients, k of isoelectrically precipitated protein (0.305-0.327 Pasⁿ) were significantly (P < 0.05) higher than that of calcium proteinates in the range ranged 0.167-0.180 Pasⁿ. Both isoelectrically precipitated proteins and calcium proteinates exhibited yield stress, however, isoelectrically precipitated S. stenocarpa protein exhibited significantly (P < 0.05) higher yield stress (0.275-0.308 Pa) than the calcium proteinates (0.148-0.165 Pa). The effect of temperature on apparent viscosity of the proteins was evaluated using an Arrhenius-type equation. The activation energies (E_a) obtained were in the range 33-51.2 and 42.6-55.5 Jmol⁻¹ for calcium proteinate and isoelectrically precipitated protein respectively.     

Comparative effect of boiling and solid substrate fermentation using the tempeh fungus (Rhizopus oligosporus) on the flatulence potential of African yambean (Sphenostylis stenocarpa L.) seeds

The tropical African yambean (AYB, Sphenostylis stenocarpa L.) is a protein-rich underutilized African legume. The presence of the flatulence- and diarrhoea-causing raffinose family oligosaccharides (RFO: raffinose, stachyose and verbascose) or α-galactosides has limited the food use of African yambean seeds. To reduce this limitation, non-traditional processing methods are required. Seeds of three varieties were (i) examined for the flatulence- and diarrhoea-causing RFO and (ii) fermented with Rhizopus oligosporus for tempeh production. The traditional tempeh production process involved dehulling, soaking in water for 24 h, boiling in water for 30 min, inoculation and fermentation. In addition, the traditional tempeh procedure was modified by using 1% citric acid solution instead of water for soaking and cooking. Comparisons with traditionally cooked beans, which involved boiling in water for 4 h, were made. Boiling seeds for 4 h resulted in 8–30% reduction of total α-galactosides in the three varieties, while the traditional tempeh procedure resulted in an almost complete loss (98%) of the same (P < 0.05). The modified procedure resulted in a bacteria-free tempeh but α-galactoside reduction was 22–39%. Both tempeh production processes were clearly more effective than was traditional cooking in reducing the flatulence potential of the AYB seeds.     

The effect of heat treatment on the in-vitro multienzyme digestibility of protein of six varieties of African yam bean (Sphenostylis stenocarpa) flour

The in-vitro multienzyme protein digestibilities of the flours of six colour varieties of African yam bean (Sphenostylis stenocarpa), made from both hulled and dehulled seeds were investigated. The multienzyme system consisted of trypsin, chymotrypsin and peptidase. Digestibilities were determined for a 15 min digestion period. Both dehulling and heat treatment improved digestibility. Comparison of flours from raw hulled seeds with those from raw dehulled seeds showed that digestibility was 7% better in the latter. Heat-treated hulled-seed flours gave a digestibility increase of 6% compared with raw flours whereas in the dehulled samples the digestibility increase of heat-treated flours over raw was 5%. Heattreated dehulled seeds were better, with a digestibility increase of 6% over the heat-treated hulled seed flours. No significant differences (P < 0.05) were observed in the digestibilities among the whole-seed flours but significant differences were observed in the dehulled-seed flours.     

Effect of ionic strength and/or pH on Extractability and physico-functional characterization of broad bean (Vicia faba L.) Protein concentrate

Protein extractability studies showed that the protein of broad bean (Vicia faba L.) was extractable at both acidic and basic pH. The percentage of pH-12 extractable protein that was precipitated at pH 4 (isoelectric point) from protein concentrate, dehulled full-fat seed flour and whole seed flour are 62.0%, 61.2% and 71.6%, respectively. Low ionic strength (μ0.4) increased the solubility of the protein in the bean concentrate at acidic pH, while at alkaline pH, increase in ionic strength (0.1–2.0) had an inverse relationship on the concentrate protein solubility. The capacity to form protein-stabilized foam was least (34%) at pH 4 and highest (97%) at pH 12. These were increased to 62% (pH 4) and 139% (pH 12) in medium with ionic strengths of 0.2 and 0.4, respectively. The foam formed was more stable at pH 4 than at the other pHs. Low ionic strength of 0.1 improved water absorption capacity but reduced it at ionic strength of 0.6.     

Biochemical composition and storage stability of a yogurt-like product from African yam bean (Sphenostylis stenocarpa)

The biochemical and storage properties of African yam bean ( Sphenostylis stenocarpa ) yoghurt-like product were evaluated. Milk extracted from the bean flour using hot water was supplemented with 4% milk protein concentrate (MPC), 0.15% dairy calcium (DC) and 0.5% gelatine (G) (singly or in combination). The milk was fermented with Streptococcus thermophilus and Lactobacillus delbrueckii spp bulgaricus at 43 °C for 3–5 h. Supplemented African yam bean (AYB) yoghurts had a gel-like consistency unlike the control (unsupplemented) sample. Total solids, protein, fat, ash, lactic acid bacterial count, lightness (L-value) and viscosity were improved by supplementation. Riboflavin and antioxidants were reduced; macroelements and thiamine were increased by 0.71–15.6% and 16.7%, respectively, because of fermentation. The stability of the product during storage at 4 °C was improved by supplementation and stirring. The pH of the supplemented product ranged from 4.45 to 4.54 and microbial counts from 2.6 × 10⁶ to 1.6 × 10⁸ during storage for not more than 3 weeks.     

Diversity of lactic acid bacteria in suan-tsai and fu-tsai, traditional fermented mustard products of Taiwan

Fu-tsai and suan-tsai are spontaneously fermented mustard products traditionally prepared by the Hakka tribe of Taiwan. We chose 5 different processing stages of these products for analysis of the microbial community of lactic acid bacteria (LAB) by 16S rRNA gene sequencing. From 500 LAB isolates we identified 119 representative strains belonging to 5 genera and 18 species, including Enterococcus (1 species), Lactobacillus (11 species), Leuconostoc (3 species), Pediococcus (1 species), and Weissella (2 species). The LAB composition of mustard fermented for 3 days, known as the Mu sample, was the most diverse, with 11 different LAB species being isolated. We used sequence analysis of the 16S rRNA gene to identify the LAB strains and analysis of the dnaA, pheS, and rpoA genes to identify 13 LAB strains for which identification by 16S rRNA gene sequences was not possible. These 13 strains were found to belong to 5 validated known species: Lactobacillus farciminis, Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, Weissella cibaria, and Weissella paramesenteroides, and 5 possibly novel Lactobacillus species. These results revealed that there is a high level of diversity in LAB at the different stages of fermentation in the production of suan-tsai and fu-tsai.     

Antioxidant and cardioprotective effects of Ilex brasiliensis: A comparative study with Ilex paraguariensis (yerba mate)

Our objective was to compare the antioxidant properties and cardiovascular effects in ischemia–reperfusion of leaves aqueous extracts of Ilex brasiliensis (B) and Ilex paraguariensis (P). In vitro systems were used to assess the antioxidant properties of the extracts. Isolated rat hearts were treated with both extracts before ischemia and myocardial function was assessed. Thiobarbituric acid reactive substances (TBARS) concentration and reduced glutathione (GSH) were also measured. B extract showed higher total phenols and ascorbic acid contents and a higher scavenging activity of peroxynitrite and ferric reducing antioxidant power (FRAP) than P extract. Postischemic systolic and diastolic functions were improved after B and P treatment. Both extracts decreased TBARS and preserved GSH content.The present study demonstrates that an aqueous extract of I. brasiliensis, similar to I. paraguariensis, protects the myocardium against ischemia–reperfusion injury and attenuates oxidative damage. These effects may be attributed to the potent antioxidant properties of the extract.     

Effects of salt, acid, and MSG on cold storage survival and subsequent acid tolerance of Escherichia coli O157:H7

The combined effects of salt, monosodium glutamate (MSG), and pH on cold storage survival and subsequent acid tolerance of Escherichia coli O157:H7 were determined. Cold storage survival was evaluated in tryptic soy broth (TSB) with combinations of pH (7.2, 5.0, or 4.0), MSG (0, 0.5, 1%) and salt (0, 2, 4%). Survival through 21 d at 5°C and acid tolerance in simulated gastric fluid were evaluated weekly. In separate experiments, strains were tested individually for the effect of growth in the presence of MSG on subsequent acid resistance and for the ability of MSG to impact growth under acid conditions. The impact of salt on cold storage survival was greater at pH 4.0 and 7.0 compared to pH 5.0. MSG did not enhance cold storage survival. The presence of MSG alone enhanced acid tolerance following cold storage at pH 5.0 and 7.2 compared to control cells. At pH 4.0, MSG alone enhanced acid tolerance compared to control cells following 21 days cold storage. Overnight growth in TSB containing MSG did not affect subsequent acid tolerance in acidified TSB (pH 2.0). The presence of MSG in TSB (37°C) did not enable growth at lower pH.     

Determining thermotolerance of fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae) and Amyelois transitella (Walker) (Lepidoptera: Pyralidae) by three different methods

Thermotolerances of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), were determined using two water-immersion methods and one dry-heat method. The two water-immersion methods were: 1) directly immersing screen tubes containing test insects in hot water (direct immersion method) and 2) immersing in hot water solid copper tubes containing insects submerged in tap water (tube immersion method). The dry heating method involved heating insects in computer-controlled heating blocks (heating block system, or HBS). Each test insect was treated at three temperature-time combinations and exposures were adjusted so that each method received the same equivalent accumulated lethal time. In five of the six tests, the HBS provided the lowest mean insect mortality among the three methods, although no statistically significant differences were observed between the direct immersion and the HBS methods. The mean insect mortality obtained with the tube immersion method was significantly higher than that from the direct immersion method and the HBS in four and three of the six temperature-time combinations, respectively. When compared with the two water-immersion methods, the HBS method yielded lower mortality data with less variation at the same mortality level, resulting in more conservative treatment recommendations.     

抑制副溶血性弧菌的乳酸菌筛选鉴定及其生物学特性研究

目的:丰富功能性乳酸菌资源库,寻找具有副溶血性弧菌拮抗能力的优良乳酸菌出发菌株。方法:采用牛津杯抑菌试验筛选具有广谱抑菌潜力的乳酸菌菌株,通过生长代谢性能、胃肠液耐受性能、耐盐性、抗生素敏感性、抑菌谱等指标探讨其生物学特性。结果:以副溶血性弧菌为指示菌,筛选得到6株乳酸菌,经形态学、生理生化、分子生物学鉴定,分别归类于类干酪乳酪杆菌、发酵黏液乳杆菌和植物乳植物杆菌。其中,类干酪乳酪杆菌A1抑菌活性最佳,24 h内菌落总数超过1×10⁹ CFU/mL,发酵液pH值稳定在4.1左右,经人工模拟胃液处理2 h后,存活率为54.61%,再经人工模拟肠液处理8 h后,存活率仍可达45.46%,经10%NaCl胁迫处理24 h后,活菌总数>1×10⁵ CFU/mL。同时,类干酪乳酪杆菌A1细菌素粗提物对13种致病菌呈良好抑菌活性,具有广谱抑菌潜力,且对8种常见抗生素未见耐药性。结论:筛选得到了能够抑制副溶血性弧菌且生物学特性优良的类干酪乳酪杆菌A1。     

Modification and properties of African yam bean (Sphenostylis stenocarpa Hochst. Ex A. Rich.) Harms starch I: Heat moisture treatments and annealing

African yam bean (Sphenostylis stenocarpa) starch was subjected to heat moisture treatments at 18% (HMT-18), 21% (HMT-21), 24% (HMT-24), 27% (HMT-27) and excess (Annealing) moisture levels. Proximate chemical composition of the starch samples revealed that the moisture content of the starches ranged between 6.7% and 12.5%. Following modification of the native starch, there was a reduction in the moisture level of the heat moisture treated starches from HMT-18 to HMT-27. However, the annealed starch (HMT-ANN) retained higher moisture content compared to native starch (AYB-Native). The carbohydrate, protein, ash, amylose and fat content reduced with all the forms of heat treatments. At the temperature range studied (60–90 °C), increasing level of heat moisture treatments reduced the solubility and swelling capacity. pH also exert a profound effect both on the solubility and the swelling of the starch. Increasing degree of alkalinity increased both solubility and swelling capacity. In the native and modified starch samples, replacement of the wheat flour by the starch resulted in increased alkaline water retention of the blends. Water absorption capacity of the starch increased with the severity of moisture treatments, while the oil absorption capacity decreased. Apart from HMT-18, there was improved gel forming capacity of all the other heat-modified starches.Pasting temperature increased after hydrothermal modifications, whereas peak viscosity (P_v), Hot Paste Viscosity (H_v), setback and breakdown values all reduced after heat moisture treatments. All the starches were of type-B viscosity.Differential scanning calorimetry studies revealed that heat moisture treatment shifted the onset temperature (T_o), peak temperature(T_p) and conclusion temperature (T_c) to higher values. The gelatinisation temperature of the annealed starch was comparable to native starch. In addition, gelatinisation band of the native starch increased progressively from HMT-18 to HMT-27. Heat moisture treatment reduced the gelatinsation enthalpy (ΔH), while the enthalpy of retrogradation(ΔH_r) increased with the storage time of the gelatinised starch. Retrogradation enthalpy of the heat moisture conditioned starches were lower than the value obtained for the native starch.X-ray diffraction studies of the starch indicated that all the starch samples showed the type-C diffraction pattern. Differences were however observed in their degree of crystallinity. Native starch exhibited the lowest crystallinity (20%) while annealed starch had the highest crystallinity (27%)Microscopy studies revealed surface indentation, formation of groves in the central region, folding of starch granules and formation of doughnut-like appearance in some of the starch samples.     

In vitro digestibility of Bacillus fermented soya bean

Bacillus fermented legume products include among others dawadawa and soumbala made from African locust bean, and natto and kinema made from soya bean. Bacillus subtilis is the dominant species involved in the fermentation. During Bacillus fermentation for 48 h of autoclaved soya bean the quantity of soluble and dialyzable matter increased from 22% and 6% up to 65% and 40%, respectively. Protein and carbohydrate degradation during fermentation of soya bean with several Bacillus spp. was investigated and appeared to be substantial during the first 18 h of fermentation resulting in the release of high levels of peptides and oligosaccharides. In vitro digestibility was increased from 29% up to 33–43% after Bacillus fermentation for 48 h. It was shown that Bacillus spp. were able to degrade soya bean macromolecules to a large extent resulting in water-soluble low molecular weight compounds. In vitro digestion of Bacillus fermented soya bean using gastrointestinal enzymes only slightly increased the amount of dialyzable matter, which clearly demonstrated the beneficial effect of Bacillus fermentation on food nutrient availability.     

Effect of a global regulatory gene, afsR2, from Streptomyces lividans on avermectin production in Streptomyces avermitilis

The global regulatory gene, afsR2, from Streptomyces lividans was previously reported to highly stimulate two structurally unrelated antibiotics, actinorhodin and undecylprodigiosin, in both S. lividans and its close relative S. coelicolor. Production of eight avermectin components was also improved in S. avermitilis: the use of wild-type S. avermitilis and its high-producing mutant, transformed by introduction of multiple copies of afsR2, increased the total avermectin productions by 2.3-fold and 1.5-fold, respectively.     

Barrier property and penetration traces in packaging films against Plodia interpunctella (Hübner) larvae and Tribolium castaneum (Herbst) adults

The barrier property of different types of plastic film (with or without pinholes) against two insects, Plodia interpunctella (Hübner) larvae and Tribolium castaneum (Herbst) adults, and the morphology of damage produced in these insects were investigated. Using a penetration apparatus, four types of plastic films varying in thickness were used for insect-penetration tests: casted polypropylene, 20 μm and 25 μm (CPP20 and CPP25); oriented polypropylene, 20 μm and 30 μm (OPP20 and OPP30); linear low-density polyethylene, 40 μm and 50 μm (LLDPE40 and LLDPE50); and polyethylene terephthalate 12 μm and 16 μm (PET12 and PET16). After being fixed and tested in the penetration apparatus, each film was cut into a disc shape and 10 holes (200 μm diameter) were made by a pin. The shape of film damage and the mouthparts of insects were observed using scanning electronic microscopy. Plodia interpunctella larvae could penetrate all films with pinholes, while T. castaneum adults were unable to penetrate any of the films tested, even those with pinholes. The penetration-percentages by P. interpunctella larvae were 38% (LLDPE40), 3% (LLDPE), 53% (CPP20), 37% (CPP25), 63% (OPP20), 43% (OPP30), 83% (PET12) and 63% (PET16). The elongation value, tensile strength and thickness of film were important factors in the penetration test. LLDPE, which has the highest elongation value and the lowest tensile strength value, was the film that best protected against insect penetration. In CPP and LLDPE films, there were many scratches and tears around the holes. In comparison, much less damage was observed around the holes in OPP and PET films. By observing the mouthparts of insects, it was determined that P. interpunctella larvae had sharper mandibles than those of T. castaneum adults.     

Effect of salt and acidic pH on the stability of virulence plasmid (pYV) in Yersinia enterocolitica and expression of virulence-associated characteristics

The stability of the Yersinia enterocolitica virulence plasmid (pYV) under different NaCl concentrations and under acidic pH conditions was investigated. Exposure of five strains representing five serotypes of pYV-bearing virulent Y. enterocolitica to 0.5, 2 and 5% NaCl and under conditions of pH 4, 5, and 6 for 24 h at 28 °C in the stationary phase did not lead to the loss of the virulent pYV from the surviving cells. At pH 3.0, the cells did not survive. Virulence assays using crystal violet binding, low-calcium response, Congo red-uptake, hydrophobicity by latex particle agglutination, and autoagglutination, as well as PCR assay to determine the presence of pYV indicated that the surviving cells were still virulent.     

Comparing predicting models for heat inactivation of Listeria monocytogenes and Pseudomonas aeruginosa at different pH

Under the same experimental conditions it has been demonstrated that whereas survival curves of Listeria monocytogenes in the range of temperatures from 54 to 62 °C followed a first-order kinetic, those of Pseudomonas aeruginosa in the range of temperatures from 50 to 56 °C were not linear showing a shoulder followed by a linear region. The first order kinetic model did not describe survival curves of P. aeruginosa. A model based on the Weibull distribution (Log₁₀(N_t/N₀)=(1/−2.303)*(t/b)ⁿ)) accurately described the inactivation kinetics of both microorganisms at the three pHs of 4, 5.5, 7.4 investigated. For both microorganisms, the b value depended on the treatment temperature and the pH of the treatment medium. Whereas for L. monocytogenes the n value was independent of the treatment conditions, for P. aeruginosa the n value depended on the pH of the treatment medium.The model based on the Weibull distribution was capable of accurately predicting the treatment time to inactivate five Log₁₀ cycles of both microorganisms at the three pHs investigated.     

Production of -aminobutyric acid (GABA) by Lactobacillus paracasei isolated from traditional fermented foods

Lactobacillus strains that accumulated γ-aminobutyric acid (GABA) in culture medium were screened to determine strains with high GABA-producing ability. One strain, NFRI 7415, which was isolated from a Japanese traditional fermented fish (funa-sushi), showed the highest GABA-producing ability among the screened strains. Identification tests (i.e., 16S rDNA sequencing and sugar assimilation ability) indicated that NFRI 7415 belongs to Lb. paracasei. The GABA production was further improved by the addition of pyridoxal phosphate to the culture medium and pH regulation of culture medium at pH 5.0. Under optimal cultivation conditions, strain NFRI 7415 produced GABA at a concentration of 302 mm when the glutamate concentration in the culture medium was 500 mm.     

沙门菌、金黄色葡萄球菌、副溶血性弧菌的选择性共增菌培养基的研制

目的 研制一种可同时对沙门菌、金黄色葡萄球菌及副溶血性弧菌进行富集的共增菌培养基SSV,达到同时检测3种食品中常见的食源性致病菌的目的。方法 根据3株菌的营养需求,选择不同的培养基组分进行单因素实验,确定选择性共增菌培养基的配方,通过OD600 nm、受损菌复苏、多重聚合酶链式反应(PCR)、培养基选择性4个方面对SSV培养基进行验证。结果 确定增菌培养基的成分为：蛋白胨10.0 g、KH₂PO₄ 1.5 g、NaCl 15.0 g、LiCl 1.0 g,Na₂S₂O₃ 5.0 g、去氧胆酸钠0.05 g、甘露醇1.0 g、丙酮酸钠5.0 g,蒸馏水1 000 mL。SSV培养基能同时富集以上3株菌,37℃培养16 h后,3株菌的菌体浓度均达到107 CFU/mL及以上;SSV培养基对于受损的目标菌有良好的复苏效果,复苏后OD₆₀₀ nm较于复苏前增长了3倍;同时多重PCR、培养基选择性也得到很好的验证。结论共增菌培养基SSV可用于同时培养沙门菌、金黄色葡...