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Thesis Analyzes Factors Responsible For The Case Of Basque Natural Cider Turning Bitter

Mon, 07/12/2010 - 10:26am
EurekAlert

Malolactic fermentation is a key part in the process of cider making, as it reduces acidity. Malic acid, a common component in fruit, undergoes a chemical transformation, turning into lactic acid. In the case of Basque natural cider (unlike with wine), after this process there is not normally any microbiological stabilisation treatment. This means that the lactic bacteria become the dominant microbiota. Some of these bacteria cause alterations that can affect the properties of the cider.

Biochemist, Mr Gaizka Garai investigated these bacteria, especially those that might make the cider bitter; this problem could affect the consumption of the drink. His PhD thesis is entitled Lactic bacteria of natural cider: involvement in alterations and probiotic potential of producer strains of (1,3)(1,2)--D-glucans.

Fructose, acidity and cold as factors

Some of the lactic bacteria that arise from fermentation metabolises glycerol and, as a consequence, produces the 3-HPA compound, which has a direct relation with an increase in bitterness. With this phenomenon in mind for his thesis, Mr Garai investigated what induced the presence of 3-HPA in Basque natural cider. As the researcher was able to clarify, the microbiota involved in the alteration of bitterness in natural cider is Lactobacillus collinoides. As regards other factors, the composition of the cider itself can cause this alteration. In fact, fructose (with a high concentration of sugar) facilitates the degradation of glycerol in the process of metabolism, in turn producing the accumulation of 3-HPA. Finally, the degree of acidity of the cider and the cold temperatures undergone in periods of maturing and storage can help the maintenance of 3-HPA.

Contains biogenic amines, but in small quantities

Lactic bacteria are not only a source of change in the bitterness; some of these are also producers of biogenic amines, which can produce toxic effects if ingested by persons with high sensitivity to them. Mr Garai studied for the first time the content of these amines in Basque natural cider. The quantities are not especially worrying. The most abundant biogenic amines that the researcher found were putrescine, tyramine and histamine, but in lower concentrations to what have been reported in drinks such as wine or beer. He also observed that there are a number of strains of biogenic amine-producing lactic bacteria, but that the most important was Lactobacillus diolivorans. This species is responsible in part for the production of histamine and tyramine. A strain of the previously mentioned Lactobacillus collinoides also produce biogenic amines; concretely, histamine.

Beneficial for the production of food

Lactic bacteria have certain beneficial properties and Mr Garai's thesis also deals with this aspect. Some of these produce exopolysaccharides, harmful for the production of drinks as they cause the product to turn oily. Nevertheless, this is not the case in food production. For example, certain lactic bacteria in natural cider are producers of the (1,3)(1,2)--D-glucan polysaccharide, which has been shown to be beneficial for both humans and animals, and valuable for the production of functional foods. Mr Garai has identified and analysed three strains amongst the lactic bacteria that produce this type of glucan in natural cider: P. parvulus CUPV1 and CUPV22 and L. suebicus CUPV221. Amongst other things, the researcher concluded that the last two show greater tolerance for gastric stress, and only L. suebicus CUPV221 can withstand the most extreme conditions of stress (pH 1,8).

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