Cooperation between Lactococcus lactis and Nonstarter Lactobacilli in the Formation of Cheese Aroma from Amino Acids

In Gouda and Cheddar type cheeses the amino acid conversion to aroma compounds, which is a major process for aroma formation, is essentially due to lactic acid bacteria (LAB). In order to evaluate the respective role of starter and nonstarter LAB and their interactions in cheese flavor formation, we compared the catabolism of phenylalanine, leucine, and methionine by single strains and strain mixtures of Lactococcus lactis subsp. cremoris NCDO763 and three mesophilic lactobacilli. Amino acid catabolism was studied in vitro at pH 5.5, by using radiolabeled amino acids as tracers. In the presence of α-ketoglutarate, which is essential for amino acid transamination, the lactobacillus strains degraded less amino acids than L. lactis subsp. cremoris NCDO763, and produced mainly nonaromatic metabolites. L. lactis subsp. cremoris NCDO763 produced mainly the carboxylic acids, which are important compounds for cheese aroma. However, in the reaction mixture containing glutamate, only two lactobacillus strains degraded amino acids significantly. This was due to their glutamate dehydrogenase (GDH) activity, which produced α-ketoglutarate from glutamate. The combination of each of the GDH-positive lactobacilli with L. lactis subsp. cremoris NCDO763 had a beneficial effect on the aroma formation. Lactobacilli initiated the conversion of amino acids by transforming them mainly to keto and hydroxy acids, which subsequently were converted to carboxylic acids by the Lactococcus strain. Therefore, we think that such cooperation between starter L. lactis and GDH-positive lactobacilli can stimulate flavor development in cheese

The Effects of Technological Modifications on the Fermentation of Borde, an Ethiopian Traditional Fermented Cereal Beverage

Four independent experiments were carried out to study the effect of modifying some steps in the technology of the four-phase traditional borde fermentation using malt and a mixture of unmalted cereals. When maize flour was substituted for maize grits in Phase I fermentation, the titratable acidity was greater throughout this phase and decreased after 24 h. Substitution with flour resulted in a higher yield, improved acceptability and extended keeping quality of borde. In addition, the wet milling at the last stage of the process could be omitted. When Phase I was omitted from the process, the starting pH at Phase II was much higher than when fermented maize from Phase I was used. Although the pH by the end of Phase II was comparable in both treatments, the borde made using fermented maize from Phase I was superior in all sensory attributes. Unmalted ingredients were heat treated in various ways and all methods were found to produce acceptable borde. However, borde from uncooked ingredients was totally unacceptable. An investigation on the effect of merging some phases of the fermentation showed that it is possible to prepare an acceptable borde using a simplified method of production. There were no marked variations in microbial load of borde from all the above treatments. It was found possible to shorten the duration and simplify the technology of borde fermentation with some variations in acceptability. Key Words: food processing; traditional fermentation; cereal beverage, borde; Ethiopia Journal of Food Technology in Africa Vol.9(1) 2004: 3-1

Indigenous processing methods and raw materials of borde, an Ethiopian traditional fermented beverage

A study of village-level processing techniques and raw materials used for the production of borde was carried out using open-ended questionnaires and on the spot interviews with producers at six localities in southern Ethiopia. The major focus of the study was on indigenous processing methods, types and proportions of ingredients, sources of energy, shelf life, sensory properties and the importance of borde for household food security. From results of the study, borde was characterized as an opaque, effervescent, whitish-grey to brown coloured beverage with a thick consistency and sweet-sour taste. It may be prepared from grits/flour of unmalted maize, barley, wheat, sorghum and/or finger millet and their malts using locally available earthenware and metal equipment. The type of unmalted cereal ingredients and amount of malt used for borde preparation varied within and between localities and were selected according to availability, price and preferences. A flow chart of borde production was constructed showing four major processing stages. The short shelf life of borde and the seasonal variations in production volume were identified as major problems for the vendors in the study areas. Keywords: indigenous methods; cereal fermentation; borde; beverage; Ethiopia J Food Tech in Africa (2002) 7, 59-6

The Effects of Technological Modifications on the Fermentation of Borde, an Ethiopian Traditional Fermented Cereal Beverage

Four independent experiments were carried out to study the effect of modifying some steps in the technology of the four-phase traditional borde fermentation using malt and a mixture of unmalted cereals. When maize flour was substituted for maize grits in Phase I fermentation, the titratable acidity was greater throughout this phase and decreased after 24 h. Substitution with flour resulted in a higher yield, improved acceptability and extended keeping quality of borde. In addition, the wet milling at the last stage of the process could be omitted. When Phase I was omitted from the process, the starting pH at Phase II was much higher than when fermented maize from Phase I was used. Although the pH by the end of Phase II was comparable in both treatments, the borde made using fermented maize from Phase I was superior in all sensory attributes. Unmalted ingredients were heat treated in various ways and all methods were found to produce acceptable borde. However, borde from uncooked ingredients was totally unacceptable. An investigation on the effect of merging some phases of the fermentation showed that it is possible to prepare an acceptable borde using a simplified method of production. There were no marked variations in microbial load of borde from all the above treatments. It was found possible to shorten the duration and simplify the technology of borde fermentation with some variations in acceptability