Evaluación del desarrollo de aminas biógenas en queso chihuahua durante la vida de anaquel.

Abstract

Food safety is a concern in the food industry since it directly affects the consumer health. Chihuahua cheese is the mature cheese of major consumption in Mexico; the maturation is realized by adding lactic microorganisms, especially Lactococcus and in some cases Streptococcus thermophiles and Lactobacillus. It has been demonstrated that mature food can develop biogenic amines because of the presence of amino descarboxilasas enzymes of the fermenter microorganisms. The consumption of histamine and tyramine can be risky for consumers, especially for those who present inhibition of monoamine oxidase enzyme._x000D_ The aim of this study was to evaluate the development of histamine and tyramine in 8 chihuahua cheeses elaborated with pasteurized milk during its shelf life. It began with the analysis of the microbiological and physical-chemical quality of the cheeses required by current regulations; selective media cultures were developed to identify bacteria in cheeses with enzymes histidine and tyrosine decarboxylase (HDC y TDC) using a synthetic broth with histidine or tyrosine added, this study was made in 4 times of the shelf life and to identify the lactic acid bacteria (BAL) with descarboxilasa enzyme in the positive tests, the biochemical system API 50 CH (Biomerieux) was used._x000D_ At the same time, the presence of histamine and tyramine was quantified by high- performance liquid chromatography (HPLC) in three different moments, at the beginning and middle of shelf life and at the product expiration. On the other hand, bacterial ADN was extracted directly from cheese to develop a methodology that includes a fat removal process. It was analyzed the presence of genes that encode the histidine and tyrosine decarboxylase enzyme by PCR reaction (Polymerase Chain) using primers previously reported for hdc and designing new primers for tdc._x000D_ The microbiological results showed that the cheeses fulfill the Mexican regulations for these products, the total account of bacteria was from 3,10 to 3,80 Log UFC/g, and coliformes from 2,6 to 3,4 Log UFC/g. Pathogenic bacteria such as Salmonella, Listeria monocytogenes or Staphylococcus aureus were not found._x000D_ The physical-.chemical studies show important variations between the marks in the concentrations of sodium, protein and fat, in some cases the values do not correspond to the ones declared in the labels. The detection of microorganisms with enzyme HDC at the end of shelf life was 37,5% of the samples and microorganisms with the enzyme TDC was 75%. Lactobacillus pentosus were identified with enzymes HDC and TDC in 3 products and L. rhamnosus with enzyme TDC in 2 products._x000D_ At the beginning of storage none of the cheeses had histamine and only 37.5% contained tyramine in concentrations from 34 to 122 mg/Kg of cheese, whereas at the end of the shelf life 75% of the cheeses had tyramine (115 to 209 mg/Kg of cheese) and 37% histamine (47-205 mg/Kg of cheese)._x000D_ Six of the eight cheeses analyzed (75%) had tdc gene whereas only 3 (37,5%) contained the hdc gene. The results of HPLC at the end of storage in the presence of tdc and hdc genes show a significant correlation of 0,001 and 0,024 respectively._x000D_ It is indispensable to decrease the formation of biogenic amines in cheeses either by pasteurization of milk, selection of the strains initiators and/or with good hygiene practices.

Date of Award	2 Dec 2013
Original language	Spanish
Supervisor	Blanca Edelia Gonzalez Martinez (Director)