Abstract
Lactic acid bacteria (LAB): Streptococcus thermophilus TA 040 andLactobacillus delbrueckii spp. bulgaricus Lb 340, were cultured in reconstituted (10%, w/v) skimmed milk with 5 or 10% (w/v) polyfloral or unifloral honey. Inoculated samples were incubated aerobically at 42°C until milk coagulation. Samples were collected at 2 h intervals and examined for biomass and pH changes. Cell viability and post-acidifying activity of both strains during 28 days of storage at 4°C were also measured. A higher increase (P<0.05) in growth and acidifying activity of S. thermophilus monocultures was observed when 10% honey was added. However, L. bulgaricus did not show such a marked increase in its growth capacity. In associated cultures, LAB growth was slightly inhibited, whereas curdling time was prolonged by an hour when 10% honey was added and yogurt acidity was moderate. Cell viability improved by 5 to 6.6% for S. thermophilus and 10% for L. bulgaricus in pure honey-sweetened cultures over 28 days of refrigerated storage. This protective effect of honey on LAB cell viability was also observed in associated cultures (10 to 12% comparatively to the control). Key words: Streptococcus thermophilus, Lactobacillus bulgaricus, honey, growth, viability.
Highlights
A greater concern in the use of natural and healthy new substances as food additives and prebiotics has been recently raised (Kneifel and Pacher, 1993)
Control Lactic acid bacteria (LAB) populations were not significantly different (P>0.05) from those obtained in the presence of 5% polyfloral or unifloral honey (Table 1)
A similar kinetic growth of S. thermophilus was observed in the presence of 5% of both honeys resulting in a curdling time of 7 h of fermentation
Summary
A greater concern in the use of natural and healthy new substances as food additives and prebiotics has been recently raised (Kneifel and Pacher, 1993). Lactic acid bacteria (LAB) are a group of related bacteria that produce lactic acid as a result of carbohydrate fermentation. These bacteria are broadly used in the production of fermented food products, such as yogurt (Streptococcus spp. and Lactobacillus spp.), cheese (Lactococcus spp.), sauerkraut (Leuconostoc spp.) and sausage (Daly et al, 1998). Lactic acid production owing to food carbohydrate consumption is one of the most de-. Sirable effects of LAB metabolic activity, inducing an important decrease in pH which may drop to as low as 4, low enough to inhibit the growth of a wide variety of microorganisms including the most common human pathogens, allowing extended shelf life in such food (Sanders, 1988; Salminen et al, 1998). The fermentation process (including microbial growth) could be self-limited because of LAB sensitivity towards such low pH
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