Ameliorarea calității în tehnologia de fabricare a iaurtului

Abstract

Iaurtul este definit ca fiind produsul din lapte coagulat obtinut prin fermentarea lactica prin actiunea microorganismelor lactice, a laptelui pasteurizat, laptelui concentrat, a smantanii pasteurizate, laptelui partial sau complet degresat si pasteurizat, cu sau fara adaos de lapte praf. Se poate prepara din lapte de vacã, oaie, bivolitã sau din amestec de lapte de la aceste specii, integral, partial sau total smântânit, pasteurizat, omogenizat sau nu, concentrat sau neconcentrat. Exista mai multe tipuri de iaurt care se fabrica cum sunt iaurtul de consistenta dura, batut, aromat, cu fructe, etc.

In tehnologia produselor lactate acide au aparut putine modificari în ultimul timp, s-au realizat putine progrese în comparatie cu cele obtinute la fabricarea altor categorii de produse lactate. Aceste produse se preteaza mai greu la mecanizarea procesului de fabricatie propriu-zis, datorita necesitatii mentinerii unei anumite consistente caracteristice fiecarui sortiment, ceea ce exclude manevrarea în vrac a produsului cu ajutorul pompelor. Tehnica noua s-a facut simtita în special în gasirea de noi tulpini de microorganisme care sa confere produsului fermentat însusiri noi, organoleptice si terapeutice superioare si de asemeni în perfectionarea mijloacelor de combatere a bacteriofagilor.

Fermentarea laptelui la fabricarea iaurtului este produsa de doua bacterii lactice asociate:Lactobacillus bulgaricus si Streptococcus thermophilus. Streptococul are temperatura optima de dezvoltare la 37 – 400C, iar lactobacilul la 45 – 500C, ultimul avand o putere acidifianta importanta (pana la 2,7% acid lactic). Cele doua bacterii se dezvolta in iaurt intr-o stransa simbioza, Lactobacillus bulgaricus favorizand dezvoltarea bacteriei Streptococcus thermophilus printr-o activitate proteolitica prin care se elibereaza o serie de aminoacizi din cazeina.

Substanţele care prelungesc durata de păstrare (durata de viaţă) a produselor alimentare, prin protejarea lor faţă de deteriorarea cauzată de oxidare (râncezire şi modificarea de culoare) sunt antioxidantii. Sunt folositi Tocoferolul (Vitamina E) si Acidul ascorbic ( Vitmina C).

La fabricarea iaurtului se folosesc utilaje pentru pasteurizare, omogenizare, concentrare, termostatare si racire. Pentru fabricarea iaurtului la care distribuirea in ambalaje se face dupa fermentare, racire si amestecare, se folosesc termostatare de racire, vane paralelipipedice cu pereti dubli avand un capac bombat, prevazut cu o deschidere acoperita de plasa; in acest fel se mentine contactul cu exteriorul si se impiedica patrunderea prafului.

Yogurt is defined as a product from coagulated milk obtained by lactic fermentation through the action of lactic microorganisms , pasteurized milk, concentrated milk, pasteurized cream,partially or completely skimmed and pasteurized milk, with or without adding milk powder. It can be prepared from cow's milk, sheep's milk, buffalos ' milk or from milk mixture from these species in whole, partially or totally skimmed milk, pasteurized, homogenized or not, unconcentrated or concentrated. There are several kinds of yogurt which are produced, such as yogurt of hard consistency, beaten, flavoured, with fruit, etc.

In the technology of acidic dairy products have appeared few changes in recent times, there have been little progress compared to those obtained in the manufacture of other categories of dairy products.

These products are hardly amenable to mechanization of the manufacturing process itself, due to the need of maintaining a certain consistency characteristic for each sort, which exclude bulk handling of the product by means of pumps. New technique was felt in particular in finding new strains of microorganisms that would confer to the fermented product new properties, superior organoleptic and therapeutic properties and also in the process of the improvement of the means for combating bacteriophages.

The fermentation of milk in the manufacturing of yogurt is produced by two associated lactic acid bacteria : Lactobacillus bulgaricus and Streptococcus thermophilus. The optimum temperature for Streptococcus to grow is at 37-40 ° C and Lactobacillus at 45-50° C, the latter having a significant acidification power (up to 2.7% lactic acid). These two bacteria are growing in yogurt in a close symbiosis.Lactobacillus bulgaricus favoring the development of bacteria through a photolytic activity which releases a series of amino acids from casein.

Substances that prolong the shelf life (life) of foods by protecting them against damage caused by oxidation (rancidity and discoloration) are antioxidants. There are used Tocopherol (Vitamin E) and ascorbic acid (Vitamin C).

For the manufacture of yogurt equipment for pasteurization, homogenization, concentration, and cooling thermostats are used. Cooling thermostatic, double-walled rectangular valves with a domed lid, equipped with an opening covered mesh are used for the production of yogurt when the distribution in packaging is made after the fermentation.; in this way it is maintained the contact with the outside and it is prevented the penetration of dust.