Microbial Ecology of Watery Kimchi

The biochemistry and microbial ecology of 2 similar types of watery (mul) kimchi, containing sliced and unsliced radish and vegetables (nabak and dongchimi, respectively), were investigated. Samples from kimchi were fermented at 4, 10, and 20 °C were analyzed by plating on differential and selective media, high‐performance liquid chromatography, and high‐throughput DNA sequencing of 16S rDNA. Nabak kimchi showed similar trends as dongchimi, with increasing lactic and acetic acids and decreasing pH for each temperature, but differences in microbiota were apparent. Interestingly, bacteria from the Proteobacterium phylum, including Enterobacteriaceae, decreased more rapidly during fermentation at 4 °C in nabak cabbage fermentations compared with dongchimi. Although changes for Proteobacterium and Enterobacteriaceae populations were similar during fermentation at 10 and 20 °C, the homolactic stage of fermentation did not develop for the 4 and 10 °C samples of both nabak and dongchimi during the experiment. These data show the differences in biochemistry and microbial ecology that can result from preparation method and fermentation conditions of the kimchi, which may impact safety (Enterobacteriaceae populations may include pathogenic bacteria) and quality (homolactic fermentation can be undesirable, if too much acid is produced) of the product. In addition, the data also illustrate the need for improved methods for identifying and differentiating closely related lactic acid bacteria species using high‐throughput sequencing methods.     

Source Tracking and Succession of Kimchi Lactic Acid Bacteria during Fermentation

This study aimed at evaluating raw materials as potential lactic acid bacteria (LAB) sources for kimchi fermentation and investigating LAB successions during fermentation. The bacterial abundances and communities of five different sets of raw materials were investigated using plate‐counting and pyrosequencing. LAB were found to be highly abundant in all garlic samples, suggesting that garlic may be a major LAB source for kimchi fermentation. LAB were observed in three and two out of five ginger and leek samples, respectively, indicating that they can also be potential important LAB sources. LAB were identified in only one cabbage sample with low abundance, suggesting that cabbage may not be an important LAB source. Bacterial successions during fermentation in the five kimchi samples were investigated by community analysis using pyrosequencing. LAB communities in initial kimchi were similar to the combined LAB communities of individual raw materials, suggesting that kimchi LAB were derived from their raw materials. LAB community analyses showed that species in the genera Leuconostoc, Lactobacillus, and Weissella were key players in kimchi fermentation, but their successions during fermentation varied with the species, indicating that members of the key genera may have different acid tolerance or growth competitiveness depending on their respective species.     

包装方式对牛排贮藏期间微生物数量和演替的影响

为研究包装方式对牛排贮藏期间的品质、微生物数量和演替的影响,牛排分别采用50% O2气调包装（50% O2＋30% CO2＋20% N2）和真空包装在0～4 ℃下贮藏21 d,并检测贮藏期间pH值、肉色、微生物数量和微生物多样性。结果表明：50% O2气调包装组比真空包装具有更好的护色效果;贮藏21 d时,与真空包装组相比,气调包装组菌落总数、乳酸菌数和假单胞菌数降低;两种包装的微生物多样性均随时间延长呈现先升高后降低的趋势,且真空包装牛排比50% O2气调包装牛排具有更复杂的微生物多样性;牛排的初始微生物主要由不动杆菌属、苍白杆菌属、栖热菌属和金黄杆菌属组成,随着贮藏时间的延长,肉食杆菌属逐渐成为真空包装牛排的优势菌群,而环丝菌属、沙雷氏菌属和乳杆菌属则成为50% O2气调包装牛排的优势菌群;贮藏7～14 d是牛排中微生物种类产生变化的关键时间点;相比于真空包装牛排,50% O2气调包装牛排中的微生物群落具有更低的糖代谢和更高的蛋白质代谢能力。本研究结果明确了不同贮藏方法下牛排的品质变化和微生物的演替规律,为定向抑制牛排中的微生物、延长产品货架期提供了参考。     

韩国泡菜制作过程中理化特性及微生物的变化

为研究韩国泡菜制作过程中品质的变化,测定其在腌制、发酵过程中一系列理化指标及微生物指标。结果表明：腌制过程中,水分含量由96.23%降低为91.34%;pH值略微下降至6.46,而总酸含量上升至2.91 g/kg;硬度降低了19.26%,降低至188 6 N;菌落总数、乳酸菌总数、酵母菌数量及大肠菌群略微上升。在发酵期间,水分含量持续降低,降至82.54%;pH值下降至3.87,而总酸含量上升至7.02 g/kg;硬度降低了68.08%至565 N;L*（亮度）值与a*（红度）值显著增加,而b*（黄度）值显著降低;菌落总数下降至3.3×102 CFU/g;乳酸菌总数达到1.3×107 CFU/g;酵母菌数量先上升后下降,最终降低为9.1×102 CFU/g;大肠菌群在第4天达到最大值93 MPN/g,随后迅速下降,低于3 MPN/g。     

低盐腊肉贮藏期间菌相和理化性质的变化

为了解低盐腊肉贮藏期间菌相和理化性质的变化情况,以同等工艺条件生产的高盐腊肉作对照,测定两种腊肉贮藏期间的pH值、水分质量分数、水分活度、食盐质量分数和硫代巴比妥酸反应物（thiobarbituric acid reactive substances,TBARS）值,并对菌落总数以及乳酸菌、微球菌和葡萄球菌、大肠菌群进行分离和计数。结果表明：两种腊肉各指标变化趋势相似,随着贮藏时间的延长,水分质量分数、水分活度和乳酸菌数量均呈下降趋势;食盐质量分数、TBARS值、微球菌和葡萄球菌数量均呈上升趋势,菌落总数先增加后减少。低盐腊肉水分质量分数、TBARS值、菌落总数均高于对照组腊肉,会导致货架期缩短。结论：降低腊肉制作过程中的食盐添加量,会引起贮藏期间腊肉的品质和菌相变化,但低盐腊肉贮藏结束时（90 d）比对照组腊肉食盐质量分数降低31.41%。     

镇巴腊肉生产过程中微生物组成及多样性变化

基于高通量测序技术,对镇巴腊肉加工过程不同阶段的微生物种群组成进行鉴定和分析,同时对细菌表型及相关功能进行预测。结果表明：镇巴腊肉生产加工过程中,真菌丰度大于细菌丰度,并随着发酵时间及加工工艺变化,微生物群落存在明显的演替;镇巴腊肉中丰度最高的细菌为厚壁菌门（Firmcutes）和变形菌门（Proteobacteria）,优势细菌属随着加工步骤推进由原料肉样品中的大肠-志贺氏菌属演替为腌制时期和熏制时期的葡萄球菌属（Staphylococcus）、嗜冷杆菌属（Psychrobacter）和乳杆菌属（Latilactobacillus）;丰度最高的真菌门为子囊菌门（Ascomycota）和担子菌门（Basidiomycota）,优势真菌属由镰刀菌属（Fusarium）和被孢霉属演替为镰刀菌属（Mortierella）和德巴利氏酵母属（Debaryomyces）;基于菌落演替变化及细菌表型和功能预测,发现镇巴腊肉在加工过程中有害微生物不断减少,利于发酵的微生物逐渐增加,促进镇巴腊肉风味物质形成。     

Impact of the Long‐Term Maintenance Method of Brewer's Yeast on Fermentation Course,Yeast Vitality and Beer Characteristics

The effect of the long‐term maintenance method used with a brewer's yeast on its technological properties was determined in laboratory fermentation trials with a 12°P all‐malt wort. The trials were performed at a constant temperature and under conditions of constant substrate concentration. Two cultures of a bottom fermenting yeast, Saccharomyces pastorianus RIBM 95, were tested — one culture was maintained by subculturing on wort agar slopes at 4°C and the other culture underwent a three year storage in liquid nitrogen at minus 196°C. Parameters under investigation included yeast vitality measured as acidification power (AP), fermentation time needed to reach an alcohol level of 4%, the yeast cell count, sedimentation of the yeast during the fermentation, and the production of beer flavour compounds in green beer. The yeast culture stored for three years in liquid nitrogen displayed a higher count of suspended cells, required a shorter time to attenuate the wort to produce 4% alcohol and produced a 1.5 to 2.5‐fold higher concentration of a number of flavour compounds. The long‐term storage method did not affect the sedimentation ability and vitality of the yeast strain tested.     

Changes in chemical quality indices during long‐term storage of palm‐olein oil under heated storage and transport‐type conditions

Six quality indices, namely free fatty acids (FFA), peroxide value (PV), anisidine value (AV), oxidative stability index (OSI), total tocopherols and headspace volatiles (hexanal, t‐2‐hexenal and t,t‐2,4‐decadienal), were evaluated in a long‐term storage trial of 52 weeks at 50 °C of palm‐olein, a monounsaturated oil. Three concentrations of copper (0.035, 0.17 and 0.69 mg kg^?1) were added. FFA values for all the sample treatments increased slightly over the storage period but remained within acceptable limits. PV of the copper‐containing samples declined initially and then remained stable up to week 40, after which it increased slightly for the 0.035 and 0.17 mg kg^?1 samples. However, PV of the control (no added copper) increased steadily to above the acceptable limit. AV of the copper‐containing samples increased much more than that of the control. OSI and total tocopherol values of the copper‐containing samples were markedly lower than those of the control. t‐2‐Hexenal did not increase during the storage period, whereas hexanal increased in the copper‐containing samples but at a slower rate than in the control. Conversely, the copper‐containing samples had high levels of t,t‐2,4‐decadienal but the control had none. AV, OSI and total tocopherols are the most valuable quality indices for assessing monounsaturated oil quality, whereas FFA, PV and headspace volatiles can be misleading. Copyright © 2003 Society of Chemical Industry     

Microbial succession and metabolite changes during the fermentation of Chinese light aroma‐style liquor

A combination of culture‐dependent and culture‐independent methods and SPME–GC–MS were used to monitor changes of bacterial and yeast communities, and flavour compounds during the fermentation process of Chinese light aroma‐style liquor. Bacillus and Lactobacillus were the main bacterial genera. Pichia anomala, Saccharomyces cerevisiae and Issatchenkia orientalis were the dominant yeast species. There was a close relationship between fermentation time and the shift of microbial community. Compared with the microbiota in the fermentation of other style liquors, higher bacterial diversity and different non‐Saccharomyces composition led to a variety of metabolites. Metabolite analysis showed that esters, acids, alcohols, aromatic compounds and phenols were the main flavour components and most of them were synthesised in the latter phase of fermentation. Principal component analysis further demonstrated that Bacillus and yeast were the most influential microorganisms in the first 10 days of fermentation, and lactic acid bacteria predominated in the later phase. Lactic acid bacteria regulated the composition of other bacteria and yeast, and synthesised flavour compounds to affect the organoleptic properties of liquor. S. cerevisiae and P. anomala were two important yeast species responsible for the characteristic aroma of liquor. These results present a comprehensive understanding of microbial interaction and potential starter cultures to produce desirable liquor quality. © 2018 The Institute of Brewing & Distilling     

The Quality Changes of Postharvest Mulberry Fruit Treated by Chitosan‐g‐Caffeic Acid during Cold Storage

This study aimed to characterize the effects of chitosan‐g‐caffeic acid (CTS‐g‐CA) on improving the quality and extending the shelf life of postharvest mulberry fruit during storage at 4 °C for 18 d. CTS‐g‐CA was enzymatically synthesized using laccase from Pleurotus ostreatus as a catalyst. The synergistic effects of CTS‐g‐CA treatment on mulberry fruit were evaluated using a co‐toxicity factor (cf). The results showed that the rotting rate of CTS‐g‐CA‐treated fruit was 37.67% (compared with that of the control at 97.67%) on day 18. The weight loss and malondialdehyde (MDA) contents of the CTS‐g‐CA‐treated mulberry fruit were significantly lower (P < 0.05) than those of the control, CA, CTS, and CA+CTS treatments. Moreover, the DPPH and ABTS radical scavenging activities of the CTS‐g‐CA treatment were both higher than those of the control. Furthermore, the CTS‐g‐CA treatment also maintained higher levels of main active substances, such as anthocyanins, ascorbic acid, polyphenols and flavones, in mulberry fruit than the other treatments. Therefore, CTS‐g‐CA could be used to improve the quality and extend the shelf life of postharvest mulberry fruit during cold storage.     

Quality aspects of fresh‐cut ‘long‐storage tomato’ as affected by package,calcium chloride and storage time

In this research, some quality changes during storage at 4 °C were assessed in fresh‐cut fruits of a ‘long‐storage tomato’ landrace, packaged in biocompostable materials (PLA Ingeo tray/NatureFlex? film) or in conventional plastics (PET tray + polypropylene film). The effects of dipping in CaCl₂ on the shelf‐life extension were also assessed. Plants were cultivated both off‐season (greenhouse) and in‐season (open field). CO₂ and O₂ concentration, fruit weight loss, firmness, colour, microbial load were measured at 0, 4, 7, 12 days of storage. Headspace gas changes and fruit weight loss were minimised in conventional package. BIO package prevented water condensation, led to max 5% weight loss and made fruits less susceptible to spoilage. Dipping in CaCl₂ induced better firmness, especially in biopackage. Off‐season fruits had overall lower quality than in‐season fruits; however, these may contribute to extend the production season, with interesting marketing implications for the agri‐food industry.     

Microbiological Properties and Biogenic Amines of Whole Pike‐Perch (Sander Lucioperca,Linnaeus 1758): A Perspective on Fish Safety During Postharvest Handling Practices and Frozen Storage

Abstract: The biogenic amines (tyramine, histamine, cadaverine, and puterscine) and microbiological properties (mesophilic, psychrotrophic, and Pseudomonas spp.) of whole pike‐perch (Sander lucioperca) was investigated during 2 d prestorage icing and 90 d frozen storage (−24 °C). At the end of ice storage, a noticeable increase only was found for puterscine level (P < 0.05), and microbial loads of fish increased in comparison with fresh fish (P < 0.05). During the frozen storage, as time passed, a continuous increase of biogenic amines and decrease of bacterial load (except for Pseudomonas spp. at the last 30 d) was detected (P < 0.05). The total contents of biogenic amines ranged from 6.24 to 91.76 μg/g during the investigated period. Puterscine was the major amine detected in pike‐perch and its concentration varied between 1.75 and 56.95 μg/g; due to a more step‐wise increase it was a good quality indicator. At the end of storage, all of the obtained values are below the tolerable maximum amounts based on available regulations. Based on biogenic amines content and microbial load, it could be concluded that pike‐perch can be consumed without any health risks after 2 d icing condition and 90 d frozen storage. Practical Application: Biogenic amines as one of the commonest forms of food intoxication occur in protein‐rich food such as fish. Short‐time icing during transportation is the simplest method to fish preserving for processing or long‐term storage. In this study formation of biogenic amines and bacterial changes in ungutted pike‐perch as highly demanded fish species for human consumption, during transportation and frozen storage was investigated. The results of the research can be advantageously used by fish industry. These findings suggest that the production and storage practices of fish in the retails condition could have acceptable food quality level.     

Use of Laser‐Etched Pouches to Control the Volume Expansion of Kimchi Packages During Distribution: Impact of Packaging and Storage on Quality Characteristics

Use of laser‐etched pouches was investigated to develop kimchi packages with gas control functions. According to the degree of laser processing, the headspace pressure, atmospheric composition, and water vapor transmission rate of the kimchi packages were measured to investigate the potential use of laser‐etched packages for kimchi. In addition, the pH, titratable acidity, organic acid, and microbial population of the packaged kimchi were examined to study the effect of packaging and storage conditions on its quality characteristics. The concentration of carbon dioxide in the pouches with a high gas transmission rate was less than that in other pouches (P < 0.05), indicating that low a carbon dioxide concentration resulted in less volume expansion. During the storage period (P < 0.05), the gas pressure in some pouches started to increase after the 15th d at 10 °C. Few differences were observed between the quality characteristics of kimchi (for example, pH, titratable acidity, organic acid, and microbial count). In addition, this study indicated that the higher the storage temperature, the more rapid the fermentation. Consequently, laser‐etched pouches demonstrate the potential for controlling the gas, which in turn maintains the quality of kimchi. The use of laser‐etched films could exert marked effects on alleviating the volume expansion or pressure build‐up in kimchi packages.