Manganese and Lactic Acid Bacteria

Abstract

Manganese (Mn), in trace quantities, is essential for growth and metabolic activities of lactic acid bacteria (LAB). The requirement for Mn has a certain degree of specifity and cannot be completely replaced by other metals. Frozen storage of LAB, species/subspecies, type of fermentable carbohydrate, interaction with other ions and chloride salts affect the extent of stimulation by Mn of LAB. Some applications of the stimulation by Mn of LAB are a bioassay for determination of this metal and its use as an aid in lactic acid fermentation of meat and plant foods. The biological effects of Mn are associated with structure/activation of enzymes, especially those involved in use of carbohydrates. Mn was also found to detoxify the superoxide radical, which is harmful to the bacterial cell, and to stabilize subcellular entities. Lactic acid bacteria (LAB) are extensively used in industrial fermentations such as those of meat (29,32), milk (37), vegetables (31), cereals (49) and other food products. LAB produce acids and other metabolites, i.e. H 2 0 2 (28), antibiotics (15), bacteriocins (45), etc. Lactic acid is moderately pleasant to the palate and has the advantage of lowering the pH, which inhibits growth of less desirable microorganisms and formation of end products by them. This inhibition by LAB is directly proportional to the rate of production of acid (2) and of other metabo-lites. A rapid reduction of pH of a fermented food reduces processing time (29,32) and gives uniform quality to the product. Thus rapid growth and acid production by LAB becomes an essential part of industrial fermentation processes. Mn is required in trace quantities for growth of most or all cells (12), including LAB (9,23,29,40). Mn accelerates growth (40,50) and acid production by LAB (29,50). Too little is known about the effects of Mn and its biological roles in LAB. The purpose of this paper is to provide an up-to-date review of the available information on Mn and LAB in a rational framework. REQUIREMENT OF MANGANESE BY LACTIC ACID BACTERIA As early as 1936, Zlataroff and Kaltschewa (53) found that Mn stimulated acid production by Streptococcus lac-tis. Moller (25) demonstrated the essential requirement for Mn by Lactobacillus plantarum. The same necessity was also noted for several lactobacilli and Leuconostoc mesenteroides (23) and for "greening" (heterofermenta-tive) lactobacilli (10). Woolley (50) found that Lac-tobacillus casei completed its growth and acid production within 12 to 16 h in the presence of Mn as compared to 40 h in its absence recording a 60 to 70% reduction in fermentation time. In this instance, Mn had an effect on the rate, and not on the extent of growth of LAB. This is contrary to the findings of Stamer et al. (40), which indicated that terminal growth as well as growth rates were dependent on the amount of Mn available to the LAB. This contradiction may stem from differences in purity of growth media or differences in experimental design. The requirement for Mn by LAB may have a certain degree of specifity. Cations such as Ca 2 + , Cu 2+ and Zn 2+ were inactive while Co 2 + , Fe 2 + and Mg 2+ (40 |xg/ml) were stimulatory to growth of "greening" lac-tobacilli (10). Mg 2 + , Ca 2+ or Sr 2+ could not replace the required Mn for growth of Lactobacillus arabinosus and Lactobacillus pentosus (23,24). The fermentation of glucose in meat by Pediococcus pentosaceus in the presence of the phenolic antioxidants BHA and BHT and cit-ric acid (each at 30 n-g/g) was the shortest (21 h) to attain pH 5.0 when Mn 2+ was added (13 |xg/g) to the meat. Other ions had little or no effect on the fermentation time. The following is the effect in decreasing order of some cations: Ca 2 + >Fe 2 + > Z n 2 + = F e 3 + >Mg 2 +. None of these ions was as efficient as Mn 2 +. For example, a pH of 5.20 was attained after 26 h of fermentation with added Ca 2+ while at the same time the treatment with Mg 2+ attained a pH of only 5.55 (29). Calcium ions were not as efficient as Mn 2+ in reducing the fermentation time of dextrose to attain pH 5.0 by several lac-tobacilli in the summer sausage (34).