Role of microbial enzymes in flavor development in foods

There are four main sources of enzymes in foods—these being the inherent enzymes, enzymes from microbial contaminants, enzymes elaborated by microorganisms added to foods, and specific enzymes added to foods. This study primarily deals with the latter two sources of enzymes in food. Although both plants and animals serve as sources of enzymes, they are not as economical or versatile sources as are enzymes obtained from microorganisms. In the meat industry, proteases are used to tenderize muscle and to obtain flavor precursors. In the preparation of cured meat products such as sausages, lipases, and proteases from bacterial cultures are utilized. Similarly, proteases and lipases are used in the dairy industry to develop flavor compounds. Proteases and amylases also have applications in the baking and milling industries where they are used to produce precursors for the nonenzymatic browning reactions. Carbohydrases such as amylase, amyloglucosidase, and glucose isomerase have found usage in the starch and syrup industry for the production of high dextrose and high fructose syrups. Other enzymes such as glucose oxidase, pectinase, and naringinase are of value to the wine and fruit juice industries. A better understanding of the mode of action of enzymes as well as the mechanisms of development of flavor compounds will further enhance the use of microbial enzymes to develop specific and desired flavors in foods.     

A decision support system for prediction of microbial spoilage in foods

Summary A method is developed to combine qualitative and quantitative information for the prediction of growth of microorganisms in foods. pH, water activity, temperature and oxygen availability of foods are coupled to growth characteristics of microorganisms. For that purpose, a database with characteristics of foods and a database of kinetic parameters of microorganisms are built. The first database has a tree structure, based on physical similarity of food products. This structure makes it possible to estimate information about a food product which is not listed by comparison with similar products at the same level of the tree or the level above. A method is developed to make an estimation of the microbial growth kinetics on the basis of models. This is done by introducing a growth factor, which can be calculated on the basis of readily available data from literature. Finally, qualitative knowledge is added. Since any bit of information can be changed, the system will give better predictions when more and more accurate information is added.     

Use of [14C]lysine to detect microbial contamination in liquid foods.

A radiometric method for microbiological control in food industries is suggested. This method, based on the labeling of cells by [14C]lysine, was tested by using nine species of yeast and two species of bacteria.     

Use of [14C]lysine to detect microbial contamination in liquid foods.

A radiometric method for microbiological control in food industries is suggested. This method, based on the labeling of cells by [14C]lysine, was tested by using nine species of yeast and two species of bacteria.     

营养相互作用对传统发酵食品微生物群落构建的推动作用研究进展

传统发酵食品是由自然接种的多微生物组成的混菌体系,了解微生物群落自发式构建的机制是认识发酵机理和调控发酵的关键。尽管大量的测序数据已经对传统发酵食品中微生物群落的结构和功能有了较为清晰的认识,但是仍然不清楚微生物群落自发式构建的机制。本文提出微生物群落是分布式的代谢系统,微生物之间的营养相互作用推动了传统发酵食品微生物群落的自发式构建。本文主要阐述了营养相互作用的概念、发生的机理以及研究方法体系,整理了传统发酵食品中微生物之间营养相互作用的研究进展,并提出了未来的研究方向。通过营养相互作用推动的传统发酵食品微生物群落的自发式构建有助于定向控制发酵过程中的微生物种类、提高生产效率和改善发酵质量。     

Development of a microbial time/temperature indicator prototype for monitoring the microbiological quality of chilled foods

A time/temperature indicator (TTI) system based on the growth and metabolic activity of a Lactobacillus sakei strain was developed for monitoring food quality throughout the chilled-food chain. In the designed system, an irreversible color change of a chemical chromatic indicator (from red to yellow) progressively occurs due to the pH decline that results from microbial growth and metabolism in a selected medium. The relation of the TTI response (color change) to the growth and metabolic activity (glucose consumption, lactic acid production, pH decrease) of L. sakei was studied. In addition, the temperature dependence of the TTI kinetics was investigated isothermally in the range of 0 to 16 degrees C and modeled with a system of differential equations. At all temperatures tested, the pH and color changes of the TTI system followed closely the growth of L. sakei, with the endpoint (the time at which a distinct visual color change to the final yellow was observed) of the TTI coinciding with a population level of 10(7) to 10(8) CFU/ml. The endpoint decreased from 27 days at 0 degrees C to 2.5 days at 16 degrees C, yielding an activation energy of 97.7 kJ/mol, which was very close to the activation energy of the L. sakei growth rate in the TTI substrate (103.2 kJ/mol). Furthermore, experiments conducted on the effect of the inoculum level showed a negative linear relationship between the level of L. sakei inoculated in the system medium and the endpoint of the TTI. For example, the endpoint at 8 degrees C ranged from 6 to 2 days for inoculum levels of 10(1) and 10(6) CFU/ml, respectively. This relationship allows the easy adjustment of the TTI endpoint at a certain temperature according to the shelf life of the food product of concern by using an appropriate inoculum level of L. sakei. The microbial TTI prototype developed in the present study could be used as an effective tool for monitoring shelf life during the distribution and storage of food products that are spoiled primarily by lactic acid bacteria or other bacteria exhibiting similar kinetic responses and spoilage potentials. Apart from the low cost, the main advantage of the proposed TTI is that its response closely matches the loss of the quality of a food product by simulating the microbial spoilage process in particular environments.     

Impact of microbial transformation of food on health - from fermented foods to fermentation in the gastro-intestinal tract

Fermentation of food components by microbes occurs both during certain food production processes and in the gastro-intestinal tract. In these processes specific compounds are produced that originate from either biotransformation reactions or biosynthesis, and that can affect the health of the consumer. In this review, we summarize recent advances highlighting the potential to improve the nutritional status of a fermented food by rational choice of food-fermenting microbes. The vast numbers of microbes residing in the human gut, the gut microbiota, also give rise to a broad array of health-active molecules. Diet and functional foods are important modulators of the gut microbiota activity that can be applied to improve host health. A truly multidisciplinary approach is required to increase our understanding of the molecular mechanisms underlying health beneficial effects that arise from the interaction of diet, microbes and the human body.