腐竹工业化加工工艺优化研究

研究豆浆的浓度、深度、加热方式及营养强化剂对腐竹提取效果的影响.结果表明,当豆浆浓度为6%,豆浆深度为5 cm时,腐竹的产率最高,成膜速度最快;采用通电加热方式蛋白提取率和成膜速度,均高于水浴加热方式;在豆浆中添加硫酸亚铁对腐竹提取效果的影响不明显;添加适量的乳酸钙可提高腐竹产率和成膜速度,降低成膜温度;同时添加硫酸亚铁和乳酸钙,可使腐竹的成膜开始温度降低6～8 ℃.     

Factors affecting the in vitro protein digestibility of chickpea albumins

In vitro protein digestibility (IVPD) of chickpea albumins and its possible relationship to their structure and the presence of trypsin inhibitor activity (TIA) have been studied. Trypsin digestion of the albumin fraction under non‐reducing conditions was incomplete, while the reduction of inter‐ and intramolecular disulphide bonds caused an improvement in the accessibility of sites susceptible to trypsin digestion. Trypsin inhibitor activity in the chickpea albumin fraction was dependent upon both temperature and heating time. Although heating the albumin fraction at 100 °C for 30 min reduced the TIA by more than 50% with respect to the initial activity, an important TIA rate was attributable to heat‐resistant trypsin inhibitor. The TIA decrease was not related to an increase in the rate of IVPD. However, we observed a significant (P ≤ 0.05) increment in IVPD in the presence of β‐ME, confirming the essential role of disulphide bonds in stabilising the protein structure of the albumin fraction. © 2000 Society of Chemical Industry     

Cowpea Flour Vitamins and Trypsin Inhibitor Affected by Treatment and Fermentation with Rhizopus microsporus

Soaking cowpeas (25°C, 24 hr) decreased folacin content but did not affect thiamin, niacin, and riboflavin. Boiling soaked seeds for 45 min sharply decreased thiamin, folacin, niacin, and riboflavin. Losses of folacin, niacin, and riboflavin were recovered during fermentation. Soaking reduced trypsin inhibitor activity (TIA) by ～20%, whereas boiling of soaked seeds decreased TIA by ～85%. A slight increase in TIA occurred in soaked, cooked cowpeas after 18 hr fermentation.     

腐竹揭皮过程中理化参数变化趋势研究

本文探讨了腐竹揭皮过程中各种理化指标的变化趋势及其对腐竹品质的影响。研究表明，在揭皮过程中蛋白质浓度和豆浆固形物浓度分别从3％和5％上升到4．4％和12％，pH值从6．5下降到6．1，腐竹中蛋白质含量从50％下降到40．1％，腐竹的韧性则从280g下降到50g。     

Comparative Effects of Ohmic,Induction Cooker,and Electric Stove Heating on Soymilk Trypsin Inhibitor Inactivation

During thermal treatment of soymilk, a rapid incorporation of Kunitz trypsin inhibitor (KTI) into protein aggregates by covalent (disulfide bond, SS) and/or noncovalent interactions with other proteins is responsible for its fast inactivation of trypsin inhibitor activity (TIA). In contrast, the slow cleavage of a single Bowman–Birk inhibitor (BBI) peptide bond is responsible for its slow inactivation of TIA and chymotrypsin inhibitor activity (CIA). In this study, the effects of Ohmic heating (220 V, 50 Hz) on soymilk TIA and CIA inactivation were examined and compared to induction cooker and electric stove heating with similar thermal histories. It was found that: (1) TIA and CIA inactivation was slower from 0 to 3 min, and faster after 3 min as compared to induction cooker and electric stove. (2) The thiol (SH) loss rate was slower from 0 to 3 min, and similar to induction cooker and electric stove after 3 min. (3) Ohmic heating slightly increased protein aggregate formation. (4) In addition to the cleavage of one BBI peptide bond, an additional reaction might occur to enhance BBI inactivation. (5) Ohmic heating was more energy‐efficient for TIA and CIA inactivation. (6) TIA and CIA inactivation was accelerated with increasing electric voltage (110, 165, and 220 V) of Ohmic heating. It is likely that the enhanced inactivation of TIA by Ohmic heating is due to its combined electrochemical and thermal effects.     

响应面法优化未浸泡脱皮大豆湿热灭酶工艺

为改善豆浆风味,采用湿热(热烫)处理对未浸泡脱皮大豆脂肪氧化酶(LOX)进行灭活。讨论了热烫温度、时间和pH值对脱皮大豆LOX酶活以及豆浆蛋白含量的影响,在此基础上设计响应面试验,通过分析得出最佳工艺：加热温度(94±2)℃、加热时间4min、pH(8±0.5),可以在保证较高蛋白含量(3.60%)的基础上使脂肪氧化酶失活。     

Application of soymilk skin as sausage wrapping for improving lipid oxidation

Yuba, the soymilk skin, was developed as edible films for sausage. Yuba (Y) were prepared with added pine-needle extract (YP) and employed to wrap sausage. Physical and mechanical properties and lipid oxidation of sausages were compared to sausages made with commercial collagen casing (C). Y films showed better transparency, oxygen-barrier properties, and UV-light barrier properties than C films (p < .05). Particularly, the addition of pine-needle extract increased DPPH activities from 31 to 48% and total phenol content from 7.52 to 14.64 mg gallic acid/g. Regarding application for sausage wrapping, Y (2.35%) and YP (2.66%) wrapped sausages with better protection against water loss during cooking compared to sausages made from C (5.84%). Especially, YP (3.57 MDA mg/kg) showed better protection against lipid oxidation for sausages than Y (4 MDA mg/kg) and C (4.62 MDA mg/kg) on day 6 after refrigerated storage. Yuba films could be employed as potential alternatives to gelatin films for manufacturing sausages.     

Denaturation Time and Temperature Effects on Solubility, Tensile Properties, and Oxygen Permeability of Whey Protein Edible Films

ABSTRACT Whey protein film solubility decreased as film-forming solution heating time and temperature increased. No differences were observed in solubility between films soaked in water at 25 °C for 24 h and 100 °C for 4 min. However, the degree of swelling was significantly larger for films soaked at 100 °C. Films became stiffer, stronger and more stretchable as film-forming solution time and temperature were increased. Oxygen permeability (OP) was lower for films made from heat-denatured whey protein than for films made from native whey protein. Results suggest that an increase in covalent cross-linking, as heat denaturation of the whey protein increases, is accountable for film water insolubility, higher tensile properties and lower OP.     

PROCESSING OF FOXTAIL MILLET FOR IMPROVED NUTRIENT AVAILABILITY

Foxtail millet grains were soaked in distilled water (1:5, w/v) for 12 h at room temperature, dehulled; dehulled and soaked; and dehulled, soaked and cooked in distilled water (1:3, w/v), and the effects of removal of polyphenols and phytate on the in vitro protein digestibility (IVPD) and availability of iron and zinc were measured. The results showed that polyphenols and phytate were decreased significantly up to 50.92 and 49.89%, respectively. The IVPD, however, increased up to 38.71%. The iron and zinc contents decreased up to 18.79 and 18.61%, respectively, but the ionizable iron and zinc were increased up to 55.45 and 80.18%, respectively. This indicated the suitability of simple processing techniques for improvement of availability of nutrients from foxtail millet.     

Influence of blanching and grinding process with hot water on beany and non-beany flavor in soymilk

A total of 8 beany odor-active compounds and 4 non-beany aroma-active compounds of traditional soymilk were identified through dynamic headspace dilution analysis (DHDA) and gas chromatography-olfactometry-mass spectrometry (GC-O-MS). To eliminate the beany flavors, soymilk was processed with hot water blanching and grinding for 2, 4, 6, 8, and 10 min with a temperature between 80 and 100 °C. A total of 5 beany odor-active compounds and 3 non-beany aroma-active compounds of this soymilk were analyzed by headspace solid phase microextraction (HS-SPME). As a result, lipoxygenase (LOX) activity gradually decreased by hot water treatment with time, and with the decrease of Lox activity, the 5 beany odor-active compounds and 3 non-beany aroma-active compounds were significantly decreased. However, the reduction in non-beany flavor compounds was smaller than for beany odor compounds. Therefore, a balance between beany and non-beany flavors can be reached in soymilk. When the soaked soybeans were blanched and ground with hot water for 2 to 6 min, the LOX activity was between 38% and 57% of the beginning activity. For these processing times, the non-beany compounds could be largely maintained. The ratio of the total peak area of the 3 non-beany aroma compounds and 5 beany flavor compounds was between 0.07 and 0.12, and the sensory scores of the aromas were higher than that of the off-flavors. Practical Application: Beany flavors in soymilk could be reduced with hot water blanching and grinding at temperature above 80 °C. However, the treatment of hot water blanching affected the non-beany aromas of soymilk. A suitable blanching and grinding time is necessary to achieve a balance of soymilk flavors.     

Formation of Volatile Sulfur-Containing Compounds by Saccharomyces cerevisiae in Soymilk Supplemented with L-methionine

The formation of volatile sulfur-containing flavor compounds from L-methionine catabolism by Saccharomyces cerevisiae EC-1118 was investigated in soymilk supplemented with this sulfur-containing amino acid with a focus on methionol (3-methylthio-1-propanol). Methionol produced from L-methionine metabolism of yeast in soymilk was extracted by solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). The effects of time (0 – 72 h), L-methionine concentration (0.05–0.20%), yeast extract concentration (0.00–0.30%), initial medium pH (4.5–6.9), and temperature (25–34°C) on the production of methionol were investigated. One-liter scale-up fermentation of soymilk by Saccharomyces cerevisiae EC-1118 was conducted for 48 h under static conditions with 0.15% of L-methionine, 0.10% of yeast extract, initial medium pH of 5.5, and temperature of 25°C, yielding 190 ppm of methionol. GC-olfactometry dilution analysis was conducted on extracts of the fermented soymilk, and no single compound was found to account for the overall odor perception. Methional (3-methylthio-1-propanal) and methionol were determined to be most potent odor-active compounds in the fermented soymilk. The fermented soy milk may serve as a complex sulfur flavor concentrate for applications in foods such as fermented soy products, enzyme-modified, and imitation cheeses.     

基于气相色谱-质谱联用技术分析酸浆豆腐加工过程中风味物质的变化

目的以酸浆豆腐为研究对象,结合气相色谱-质谱联用法(gas chromatography-mass spectrometry,GC-MS)优化酸浆豆腐不同加工阶段中挥发性风味物质的捕获方法,对酸浆豆腐的加工阶段进行分类。方法采用顶空-固相微萃取法(head space-solid phase microextraction,HS-SPME)结合GC-MS对风味物质进行检测,优化风味物质捕获方法,内标法进行定量,结合聚类分析对加工阶段进行分类。结果不同批次酸浆豆腐中风味物质变化具有较高的稳定性,酸浆豆腐加工过程中共鉴定出90种挥发性风味物质,制浆、煮浆、点浆、蹲脑10 min、蹲脑20 min和压制工序分别鉴定出27、25、32、39、45和22种挥发性风味物质,主要为醛类、酮类、醇类等风味物质。对加工过程中风味物质进行聚类分析发现:适当延长煮浆与蹲脑时间,可促进更多良好风味物质的形成。结论该方法操作简单,适合酸浆豆腐中风味物质的测定且稳定性好,在后续实验中可进一步对加工工艺进行调控。     

Rapid Heating of Alaska Pollock and Chicken Breast Myofibrillar Proteins as Affecting Gel Rheological Properties

Surimi seafoods (fish/poikilotherm protein) in the U.S.A. are typically cooked rapidly to 90+°C, while comminuted products made from land animals (meat/homeotherm protein) are purposely cooked much more slowly, and to lower endpoint temperatures (near 70 °C). We studied heating rate (0.5, 25, or 90 °C/min) and endpoint temperature (45 to 90 °C) effects on rheological properties (fracture, small strain) of washed myofibril gels derived from fish (Alaska pollock) compared with chicken breast at a common pH (6.75). This was contrasted with published data on gelation kinetics of chicken myosin over the same temperature range. Heating rate had no effect on fracture properties of fish gels but slow heating did yield somewhat stronger, but not more deformable, chicken gels. Maximum gel strength by rapid heating could be achieved within 5 min holding after less than 1 min heating time. Dynamic testing by small strain revealed poor correspondence of the present data to that published for gelling response of chicken breast myosin in the same temperature range. The common practice of reporting small‐strain rheological parameters measured at the endpoint temperature was also shown to be misleading, since upon cooling, there was much less difference in rigidity between rapidly and slowly heated gels for either species.     

Trout skin gelatin-based edible film development

Edible biopolymer films were developed from gelatin extracted from trout skin (TSG) using thermal protein denaturation conditions and plasticizer (glycerol) concentration as variables. The amino acid composition of the TSG, elastic modulus, viscous modulus, and the viscosity of film-forming solutions, and tensile properties, water vapor permeability, solubility in water, and color of TSG-based films were determined. A 6.8% (w/w, wet basis) trout skin-extracted gelatin solution containing 9, 17, or 23% (w/w, dry basis) glycerol was heated at 80, 90, or 100 °C for 30, 45, or 60 min to prepare a film-forming solution. TSG can be characterized as a gelatin containing high contents of methionine and aspartic acid. The gelation temperature of the film-forming solution was 7 °C and the solution was subjected to heating to form a stable matrix for a film. Increased heating time of the film-forming solution reduced the film solubility (P < 0.05). Heating at 90 °C for 30 min was suggested as the requirement for film formation. As the concentration of glycerol in the film increased, film strength and moisture barrier properties decreased, while film stretchability increased (P < 0.05). Trout skin by-products can be used as a natural protein source for fabricating biopolymer films stable at ambient conditions with certain physical and moisture barrier properties by controlling thermal treatment conditions and glycerol concentrations. Practical Application: The fishing industry produces a significant amount of waste, including fish skin, due to fish processing. Trout skin waste has potential value as a protein source that can be used to form biopolymer edible films for packaging low and intermediate water activity food products, and thus may have practical applications in the food industry, which could be one way to cut waste disposal in the trout processing industry.     

Sensory evaluation and in vitro protein digestibility of mung bean as affected by cooking time

Heat treatment is particularly important in the preparation of mung bean for consumption, from the point of view not only of acceptability but also of improvement on protein digestibility. Sensory evaluation of cooked mung bean in terms of taste, colour, aroma and texture has an organoleptic panel indicated that there was no significant difference (P < 0.05) between mung bean cooked for 25, 30, 35, 40 and 45 min. An in vitro protein digestibility assay was used to examine the effect of cooking time on protein digestibility. The applied non-linear mathematical model indicated a high correlation coefficient between experimental and predicted data (R² ≥ 0.999). A maximum improvement in in vitro protein digestibility (IVPD) of 4.83% was obtained by cooking for 38.6 min. No remarkable changes in most amino acids were found between raw and cooked samples except that tryptophan was decreased by 4.69% and a 10.29% loss of threonine occurred with the optimum cooking time. © 1999 Society of Chemical Industry     

Supplementation of pearl millet flour with soybean protein: effect of cooking on in vitro protein digestibility and essential amino acids composition

In vitro protein digestibility (IVPD) and amino acids profile of pearl millet (Dempy cultivar) supplemented with soybean protein (5–15%) were investigated. Supplementation of dempy flour with soybean protein steadily decreased IVPD with increasing the portion of soybean in the blend. The in vitro protein digestibilities of the cooked supplemented dempy flours were higher when compared with the raw ones, whereas the highest value was that of the 5% soybean protein. All essential amino acids of dempy flour were enriched on supplementation with soybean protein. The levels of amino acids increased with increasing the amount of soybean protein in the blend. Essential amino acids in dempy supplemented with 15% soybean are comparable to those in the FAO reference pattern. Supplementation increased significantly lysine to 1.5–2.4 folds. Essential amino acids content remained higher in the cooked composite flours when compared with the cooked native dempy flour.     

Improved Acid, Flavor and Volatile Compound Production in a High Protein and Fiber Soymilk Yogurt-like Product

The effects of added caseinate (CAS), casein hydrolyzate (CASHY) and whey protein hydrolyzate (WPHY) on acid, flavor and volatile compound production in a high protein and fiber soymilk yogurt-like product were studied. High protein and fiber soymilk, produced by blending soaked, boiled and dehulled soybeans with Swiss cheese whey ultrafiltration permeate, was fermented with a mixed S. thermophilus and L. bulgaricus yogurt culture. The concentrations of lactic acid, key volatile compounds, i.e., acetaldehyde, acetone, and diacetyl, and the flavor and texture of the resulting soymilk based yogurt formulated with added CAS or CASHY were comparable to those in a milk yogurt control.     

Some Antinutritional Factors in Moringa peregrina (Al-Yassar or Al-Ban) and Soybean Products

Moringa peregrina and soybean defatted flours, protein concentrates, and isolates were assayed for trypsin (TIA) and α-amylase (AIA) inhibitor activities, phytic acid, tannin and chlorogenic acid contents, and in vitro protein digestibility (IVPD). TIA in M. peregrina defatted flour (MDF) was lower (P < 0.05) but more heat resistant than in soybean. AIA in MDF was lower than in soybean and inhibited pancreatic amylase more than bacterial amylase. Some M.peregrina products were higher in phytic acid but lower in chlorogenic acid than soybean. Tannin was low in all samples. IVPD was slightly lower for M.peregrina than for soybean.     

Effect of thermal pretreatment of raw soymilk on the gel strength and microstructure of tofu induced by microbial transglutaminase

The influence of thermal pretreatment of raw soymilk on the gel hardness and microstructure of tofu, induced by microbial transglutaminase (MTGase), was investigated in this paper. Modulated differential scanning calorimetry analysis showed that individual proteins in soymilk were to a various extent denatured by different thermal pretreatments. The viscosity of the soymilk and the gel hardness of MTGase-induced tofu were more highly related with the heating rate (up to 90 °C) than the mode of heating. At any enzyme concentration of MTGase, the tofus prepared from soymilk heated at 75 °C for 10 or 30 min showed highest gel hardness among all tested ones (P?0.05). Scanning electron microscopy analysis indicated that the microstructure of the tofu from soymilk heated at 75 °C for 30 min had a unique coral-like structure, much more continuous and homogenous than that from soymilk at 95 °C for 5 min. These results confirmed that the appropriate heat pretreatment (e.g. in the present, at 75 °C for 10-30 min) remarkably improved the gel strength of tofu by means of MTGase, and strengthened the tofu gel structure.     

Effect of inulin on the rheological properties of silken tofu coagulated with glucono-δ-lactone

This study investigated the rheological properties of inulin-containing silken tofu coagulated with glucono-δ-lactone (GDL) upon heating. Inulin (Raftiline^® HP-gel) was added to a soy protein isolate-enriched cooked soymilk at 0%, 1%, 2%, 3% and 4% (w/v) levels along with 0.4% (w/v) GDL to prepare acid-induced silken tofu. Gelation was induced by heating the soymilk mixture from 20 to 90 °C at a constant rate (1 °C/min) or isothermally at 90 °C for 30 min. The gelling properties were measured with dynamic small-deformation mechanical analysis and static large-deformation compression tests. The rheological changes in soymilk during gelation were dependent upon both the pH decline (hydrolysis of GDL) and the specific temperature of heating. Control samples heated to 50 °C, with the pH lowered to 5.95, started to gel, showing a rapid increase in storage (G′) and loss (G″) moduli afterwards. The addition of 2% inulin lowered the on-set gelling temperature by 2.8 °C and improved (P < 0.05) both rheological parameters of the tofu gel as well as hardness and rupture force (textural profile analysis) of the formed silken tofu. The results indicated that inulin enhances the viscoelastic properties of GDL-coagulated silken tofu, and the textural effect of inulin is an added benefit to its current application mainly as a prebiotical ingredient in food.