描述性分析在食品感官评定中应用进展

该文简介食品科学领域所应用几种描述性分析方法,如定量描述性分析、蛛网描述性分析、属性引用次数法、时间―强度曲线描述性分析法、自由选择描述法等,举例其应用,并分析描述性分析发展趋势。     

Probiotics for the young and the not so young

Although interest in the effects of the intestinal flora on health dates from the beginning of the 20th century, controlled clinical trials did not begin until its end. Oral administration of probiotic lactobacilli has been shown to alleviate and prevent atopic eczema. Similar effects were accomplished by administering fructose and glucose oligosaccharides (prebiotics) which encouraged the proliferation of endogenous lactobacilli and bifidobacteria. Nonpathogenic Escherichia coli has been shown to protect premature infants from infection. Twenty years later, infants given this E. coli were still found to be less allergic. Meta-analyses have confirmed that Lactobacillus rhamnosus strain GG prevents and treats rotavirus diarrhoea. By reversing the changes in bowel flora which occur with age comes the prospect of rejuvenating ageing immune systems, preventing Clostridium difficile infections and bowel cancer, thereby fulfilling the early promise of prolongation of life.     

Fermentation of heated gluten systems by gut microflora

The Maillard reaction causes changes to protein structure and occurs in foods mainly during thermal treatment. Melanoidins, the final products of the Maillard reaction, may enter the gastrointestinal tract, which is populated by different species of bacteria. In this study, melanoidins were prepared from gluten and glucose. Their effect on the growth of faecal bacteria was determined in culture with genotype and phenotype probes to identify the different species involved. Analysis of peptic and tryptic digests showed that low molecular mass products are formed from the degradation of melanoidins. Results showed a change in the growth of bacteria. This in vitro study demonstrated that melanoidins, prepared from gluten and glucose, affect the growth of the gut microflora.     

Apple pieces as immobilization support of various microorganisms

The biocatalyst prepared by immobilization of Saccharomyces cerevisiae strain AXAZ-1 on apple pieces was used for fermentation of grape must both in batch and continuous system. The immobilized yeast showed an important operational stability without any decrease of its activity. In continuous process, the bioreactor was operated for 95 days without any diminution of the ethanol productivity. Concentrations of higher and amyl alcohols were low indicating an improved quality product.Apple pieces were also used as support for immobilizing Kluyveromyces marxianus IMB3 for high-temperature (45 °C) wine-making. The fermented grape must contained 3-4% alcohol and semi-sweet wines were produced by the addition of potable alcohol.Preliminary sensory evaluation of the produced wines ascertained the fruity aroma and the overall improved quality compared to other commercially available products.Lactobaccillus casei cells immobilized on apple pieces were used for probiotic, fermented milk and lactic acid production. Apple-supported L. casei used for successive fermentation batches of whey proved to be very effective and suitable for food-grade lactic acid production. The immobilized biocatalyst was also used for milk fermentation and was able to ferment after storage for 15, 98 and 129 days at 4 °C, while no infection was reported during storage periods.     

Investigation of the factors influencing the survival of Bifidobacterium longum in model acidic solutions and fruit juices

The survival of Bifidobacterium longum NCIMB 8809 was studied during refrigerated storage for 6 weeks in model solutions, based on which a mathematical model was constructed describing cell survival as a function of pH, citric acid, protein and dietary fibre. A Central Composite Design (CCD) was developed studying the influence of four factors at three levels, i.e., pH (3.2–4), citric acid (2–15 g/l), protein (0–10 g/l), and dietary fibre (0–8 g/l). In total, 31 experimental runs were carried out. Analysis of variance (ANOVA) of the regression model demonstrated that the model fitted well the data. From the regression coefficients it was deduced that all four factors had a statistically significant (P < 0.05) negative effect on the log decrease [log₁₀N_{0 week}−log₁₀N_{6 week}], with the pH and citric acid being the most influential ones. Cell survival during storage was also investigated in various types of juices, including orange, grapefruit, blackcurrant, pineapple, pomegranate and strawberry. The highest cell survival (less than 0.4 log decrease) after 6 weeks of storage was observed in orange and pineapple, both of which had a pH of about 3.8. Although the pH of grapefruit and blackcurrant was similar (pH ∼3.2), the log decrease of the former was ∼0.5 log, whereas of the latter was ∼0.7 log. One reason for this could be the fact that grapefruit contained a high amount of citric acid (15.3 g/l). The log decrease in pomegranate and strawberry juices was extremely high (∼8 logs). The mathematical model was able to predict adequately the cell survival in orange, grapefruit, blackcurrant, and pineapple juices. However, the model failed to predict the cell survival in pomegranate and strawberry, most likely due to the very high levels of phenolic compounds in these two juices.     

Effect of fermentation by pure and mixed cultures of Streptococcus thermophilus and Lactobacillus helveticus on isoflavone and B-vitamin content of a fermented soy beverage

Enhancement of nutritional or vitamin content of foods is commonly touted as a major benefit of probiotics. In this paper, we examined the ability of three probiotic bacteria either alone or in combination to enhance nutritional content. Pure and mixed cultures of Streptococcus thermophilus ST5 and Lactobacillus helveticus R0052 or Bifidobacterium longum R0175 were used to prepare fermented soy beverages. The effects of strain, acidification and mixed cultures on the deconjugation of soy isoflavones were examined. Acidification to pH 4.7 alone resulted in a 7% drop in isoflavone levels. Deconjugation levels varied between the different glucosides. Fermentation by L. helveticus R0052 resulted in the 50% reduction in total glucosides with O-malonyl glucosides being reduced 64%. Fermentation by S. thermophilus ST5 or B. longum R0175 had no significant effect on isoflavone levels. Combining a S. thermophilus strain with a L. helveticus culture reduced the effectiveness of the latter. Fermentation did not significantly modify vitamin B1 or B6 levels.     

合成气发酵产乙醇微生物菌群富集及微生物区系研究

为获得能够利用合成气发酵产乙醇的新菌株,分别从长臂猿、骆驼、豪猪和戴冕鹤4种动物粪便中连续富集培养获得了4个菌群（G-fm18、C-fm18、H-fm18、BP-fm18）,首先考察了种子液中少量木糖对于菌群合成气发酵的影响,然后对富集菌群进行变性梯度凝胶电泳（DGGE）微生物群落结构分析。结果表明,4种菌群均能够利用合成气发酵产生乙醇,且随着传代次数的增多,乙醇生产性能逐渐加强。种子液中携带的少量木糖可以显著促进合成气发酵菌群（菌株）的乙醇产量,种子液不离心后接种发酵的情况下,菌群G-fm18的乙醇产量最高为253.87 mg/L,约为离心发酵后乙醇产量的8倍。菌群G-fm18中主要含有一种不可培养细菌和芽孢杆菌;菌群C-fm18中主要含有一种不可培养细菌、芽孢杆菌、柠檬酸杆菌和瘤胃球菌;菌群H-fm18中主要含有肠杆菌;菌群BP-fm18中主要含有一种不可培养细菌、梭菌和气单孢菌。     

Amyl alcohols as compounds indicative of raw cocoa bean quality

 Amyl alcohols were isolated from raw cocoa beans by steam distillation and quantified by means of gas chromatography. Concentration ratios between primary and secondary amyl alcohols and between alcohols, aldehydes and acetates were calculated. These ratios indicate the fermentation degree and possible staling of cocoa beans. Hence, flavour quality of raw cocoa beans may be measured and the method used for industrial quality control. Received: 27 October 1995/Revised version: 25 March 1996     

Amyl alcohols as compounds indicative of raw cocoa bean quality

 Amyl alcohols were isolated from raw cocoa beans by steam distillation and quantified by means of gas chromatography. Concentration ratios between primary and secondary amyl alcohols and between alcohols, aldehydes and acetates were calculated. These ratios indicate the fermentation degree and possible staling of cocoa beans. Hence, flavour quality of raw cocoa beans may be measured and the method used for industrial quality control. Received: 27 October 1995/Revised version: 25 March 1996     

梭子蟹腐败菌菌相的初步分析

对梭子蟹冷藏(0～4℃)过程中体内的腐败菌菌相变化进行初步分析,对菌落形态、颜色、细胞形状、是否形成芽孢、有无鞭毛、鞭毛是否极生以及一系列的生理生化特性进行分析,实验结果表明:新鲜梭子蟹体内的细菌菌群组成为微球菌属(Micrococcus)、葡萄球菌属(Staohylococcus)、黄杆菌属(Flacobacterium)、弧菌属(Vibrio)。梭子蟹经冷藏半个月后,梭子蟹体内的细菌菌群主要是杆菌,包括黄单胞菌属(Xanthomonas)和黄杆菌属(Flacobacterium)。