J. Rossi

ANTIMOULD ACTIVITY OF SOURDOUGH LACTIC ACID BACTERIA: IDENTIFICATION OF A MIXTURE OF ORGANIC ACIDS PRODUCED BY LACTOBACILLUS SANFRANCISCO CB1

Abstract Sourdough lactic acid bacteria, cultivated in wheat flour hydrolysate, produced antimould compounds. The antimould activity varied greatly among the strains and was mainly detected within obligately heterofermentative Lactobacillus spp. Among these, Lb. sanfrancisco CB1 had the largest spectrum. It inhibited moulds related to bread spoilage such as Fusarium, Penicillium, Aspergillus and Monilia. A mixture of acetic, caproic, formic, propionic, butyric and n-valeric acids, acting in a synergistic way, was responsible for the antimould activity. Caproic acid played a key role in inhibiting mould growth.

Characterization of non-starter lactic acid bacteria from Italian ewe cheeses based on phenotypic, genotypic, and cell wall protein analyses.

ABSTRACT Non-starter lactic acid bacteria (NSLAB) were isolated from 12 Italian ewe cheeses representing six different types of cheese, which in several cases were produced by different manufacturers. A total of 400 presumptive Lactobacillus isolates were obtained, and 123 isolates and 10 type strains were subjected to phenotypic, genetic, and cell wall protein characterization analyses. Phenotypically, the cheese isolates included 32% Lactobacillus plantarumisolates, 15% L. brevis isolates, 12% L. paracasei subsp. paracasei isolates, 9% L. curvatus isolates, 6% L. fermentum isolates, 6%L. casei subsp. casei isolates, 5% L. pentosus isolates, 3% L. casei subsp.pseudoplantarum isolates, and 1% L. rhamnosusisolates. Eleven percent of the isolates were not phenotypically identified. Although a randomly amplified polymorphic DNA (RAPD) analysis based on three primers and clustering by the unweighted pair group method with arithmetic average (UPGMA) was useful for partially differentiating the 10 type strains, it did not provide a species-specific DNA band or a combination of bands which permitted complete separation of all the species considered. In contrast, sodium dodecyl sulfate-polyacrylamide gel electrophoresis cell wall protein profiles clustered by UPGMA were species specific and resolved the NSLAB. The only exceptions were isolates phenotypically identified asL. plantarum and L. pentosus or as L. casei subsp. casei and L. paracaseisubsp. paracasei, which were grouped together. Based on protein profiles, Italian ewe cheeses frequently contained four different species and 3 to 16 strains. In general, the cheeses produced from raw ewe milk contained a larger number of more diverse strains than the cheeses produced from pasteurized milk. The same cheese produced in different factories contained different species, as well as strains that belonged to the same species but grouped in different RAPD clusters.

The sourdough microflora. Interactions between lactic acid bacteria and yeasts: metabolism of carbohydrates

Interactions betweenLactobacillus brevis subsp.lindneri CB1,L. plantarum DC400,Saccharomyces cerevisiae 141 andS.exiguus M14 from sourdoughs were studied in a co-culture model system using a synthetic medium. The lack of competition for maltose whenS.exiguus M14 was present in co-culture with each of the lactic acid bacteria (LAB) enhanced the bacterial cell yield and lactic and acetic acid production.L.brevis subsp.lindneri CB1 resting cells hydrolysed maltose and accumulated glucose in the medium, allowing the growth of maltose negative yeast.S.cerevisiae 141 competed greatly with each of the LAB for glucose and only withL.plantarum DC400 for fructose, causing a decrease in the bacterial cell number and in acid production. As a result of the glucose and fructose availability after the invertase activity of both yeasts,L.plantarum DC400 grew optimally in the presence of sucrose as a carbon source. All of the interactions indicated were confirmed by studying the behaviour of the co-cultures in wheat flour hydrolysate.

Interactions between yeasts and bacteria in the smear surface-ripened cheeses

In the initial phase of ripening, the microflora of bacterial smear surface-ripened cheeses such as Limburger, Taleggio, Brick, Münster and Saint-Paulin and that of surface mould-ripened cheeses such as Camembert and Brie may be similar, but at the end of the ripening, bacteria such as Brevibacterium spp., Arthrobacter spp., Micrococcus spp., Corynebacterium spp. and moulds such as Penicillium camemberti are, respectively, the dominant microorganisms. Yeasts such as Candida spp., Cryptococcus spp., Debaryomyces spp., Geotrichum candidum, Pichia spp., Rhodotorula spp., Saccharomyces spp. and Yarrowia lipolytica are often and variably isolated from the smear surface-ripened cheeses. Although not dominant within the microorganisms of the smear surface-ripened cheeses, yeasts establish significant interactions with moulds and especially bacteria, including surface bacteria and lactic acid bacteria. Some aspects of the interactions between yeasts and bacteria in such type of cheeses are considered in this paper.

Volatile compound and organic acid productions by mixed wheat sour dough starters: influence of fermentation parameters and dynamics during baking

Lactobacillus brevis subsp. lindneri CB1, Lactobacillus plantarum DC400 and Saccharomyces cerevisiae 141 or Saccharomyces exiguus M14 were used as starters to produce wheat sour dough breads. Sour doughs with higher relative percentage of yeast fermentation products (1-propanol, 2-methyl-1-propanol, 3-methyl-1-butanol and ethanol) and with higher total peak area of volatile compounds, or with a more complete profile (higher amounts of ethylacetate and lactic and acetic acids, and the presence of carbonyl compounds) were produced by the associations between lactic acid bacteria (LAB) and S. cerevisiae 141 or S. exiguus M14, respectively. Low temperature (25°C) and sour dough firmness (dough yield 135) were appropriate for LAB souring activities but limited yeast metabolism. Raising the temperature to 30°C and semi-fluid sour doughs gave more complete volatile profiles. Flour ash content from 0·55–1% positively influenced the total amount of volatiles and lactic and acetic acid productions. While at 3 h the sour dough was mainly characterized by iso-alcohols, an increase of leavening time up to 9 h gave a total amount of volatiles about three times higher than that at 5 h and strengthened the LAB contribution. The additions of fructose and citrate to the dough enhanced the acetic acid and volatile synthesis by LAB, respectively. After baking, the ethanol disappeared, 2-methyl-1-propanal was synthetized, lactic and acetic acids remained constant, the total amount of volatiles was reduced to a level

Microbiology and biochemistry of Fossa (pit) cheese

A microbiological and biochemical characterization of the Fossa (pit) cheese is reported. The cheeses analysed showed di!erences for the protocol of production and type of cheese-milk used (bovine or ovine). The total number of mesophilic bacteria and the number of specic microbial groups di!ered among the cheeses. Lactococci used as starters were found at very low numbers. Non-starter lactic acid bacteria (NSLAB) such as Lactobacillus plantarum, Lb. curvatus and Lb. paracasei subsp. paracasei were found at high numbers (5.8}7.8 log cfu g~1). Cheeses produced from pasteurized or raw milks and using lactococci as starters or not showed similar microbiological and biochemical characteristics. High concentrations of NaCl-in-moisture (ca. 11.5%) and a low value of a 8 (ca. 0.850) negatively in#uenced the microbial content and proteolysis. The ratio pH 4.6-soluble N/total N (23.6}39.1%) and the concentration of free amino acids (11.37}41.06 mg g~1) were very high and varied with cheeses. Fossa cheeses which contained the highest number of NSLAB also had the highest concentration of amino acids. The principal amino acids were glutamic acid, valine, leucine and lysine. Urea-PAGE electrophoresis of the pH 4.6 insoluble and soluble fractions di!erentiated the cheeses. Apart from the variations in the protocol of production, the RP-HPLC of the ethanol-soluble fraction showed a peptide prole which was common to all the cheeses. Especially cheeses which had the highest concentrations of free amino acids and the highest number of NSLAB, also contained the highest aminopeptidase, dipeptidase and iminopeptidase activities. Fossa cheeses also showed a moderate lipolysis which varied among the samples: total free fatty acids ranged from 578 to 1676 mg kg~1. The highest concentrations were found independently of the milk used. The principal fatty acids were butyric, caproic, palmitic and oleic acids. Sensory evaluation of the Fossa cheeses showed di!erences especially related to the extent of proteolysis. ( 2000 Elsevier Science Ltd. All rights reserved.

Maltose-fructose co-fermentation by Lactobacillus brevis subsp. lindneri CB1 fructose-negative strain

The Lactobacillus brevis subsp. lindneri CB1 fructose-negative strain utilized fructose in co-fermentation with maltose or glucose. Compared to the maltose (17 g/l) fermentation, the simultaneous fermentation of maltose (10 g/l) and fructose (7 g/l) increased cell yield (A620from 2.6 to 3.3) and the concentrations of lactic acid and especially of acetic acid (from 2.45 g/l to 3.90 g/l), produced mannitol (1.95 g/l) and caused a decrease in the amount of ethanol (from 0.46 g/l to 0.08 g/l). The utilization of fructose depended on the continuous presence of maltose in the growth medium and the two carbohydrates were consumed in a molar ratio of about 2:1. The presence of tagatose (a fructose stereoisomer) partially inhibited fructose consumption and consequently caused a decrease of the end products of the co-metabolism. Since maltose was naturally present during sourdough fermentation, the addition of only 6 g fructose/kg wheat dough enabled the co-fermentation of maltose and fructose by L. brevis subsp. lindneri CB1. A higher titratable acidity and acetic acid concentration, and a reduced quotient of fermentation (2.7) were obtained by co-fermentation compared with normal sourdough fermentation. Some interpretations of the maltose-fructose co-fermentation are given.