Βιοδιεργασίες στην παραγωγή προβιοτικών γαλακτοκομικών προϊόντων με ακινητοποιημένα γαλακτικά βακτήρια σε πριβιοτικούς φορείς

Worldwide food market is displaying an increased demand for functional foods that contain technologically developed novel ingredients that have beneficial health effects. In addition, new approaches have been developed in order to satisfy the consumer’s needs for healthier, safe and high quality dairy products. Probiotic dairy products are among the main suggested types of food that can provide numerous nutritional benefits to consumers. Various studies have reported that the use of probiotic bacteria, especially Lactobacilli strains, can offer health benefits to the host when administered at appropriate amounts (106-107 CFU/g). Thus, the main objective of the present thesis was the production of novel immobilized probiotic biocatalysts that can be used for functional dairy food production. More specifically, prebiotic carriers (wheat bran, delignified wheat bran, corn, sea buckthorn berries and yellow split peas) were used for the immobilization of lactobacilli and after that for the production of probiotic dairy products. All immobilized biocatalysts and free cells were previously freeze dried without any cryoprotectants and tested for their viability. All prebiotic carriers were proved to have a protective effect on the viability of immobilized lactobacilli cells. The effect of the immobilized biocatalysts to the physicochemical, microbiological, volatile and sensory characteristics of the produced dairy products was also studied. In first, white brine cheeses were produced. The probiotic microorganism L. casei ATCC 393 was immobilized on wheat bran, delignified wheat bran, corn, sea buckthorn berries and yellow split peas for the production of Feta type brine cheeses. For comparison reasons free cells of L. casei were also used for cheese production. Wheat bran is a mills by-product with a high nutritional value and prebiotic effects. Delignification of wheat bran resulted to higher immobilized cell viability of L. casei when incorporated into Feta type cheese products. Based on this observation, the potentially probiotic strain L. paracasei K5, isolated from Greek dairy products, was also immobilized on delignified wheat bran and used for the production of white brine cheeses. All immobilized biocatalysts incorporated in white brine cheeses imparted exceptional organoleptic characteristics to the manufactured products with high lactobacilli viability (>106 CFU/g). No pathogens were detected in white brine cheeses after the 60th storage day so the cheeses were ready for consumption. Moreover, sea buckthorn berries used as cell carrier introduced antimicrobial attributes and minimized earlier spoilage in Feta cheese compared with the other immobilized biocatalysts probably due to their higher terpene content. Secondly, probiotic yogurts were produced by incorporation of free and/or immobilized L. casei and L. bulgaricus cells on wheat bran and delignified wheat bran. At first, L. casei and L. bulgaricus cells were grown in cheese whey after the removal of protein content. This procedure was proved to be slower than the classic lactobacilli cultivation but is certainly a cheaper process since an industrial by-product is used, i.e. whey, which is a major liquid effluent of the dairy industry. Moreover, the immobilization process was also carried out in whey giving good quality immobilized biocatalysts. After freeze drying, the immobilized L. casei and L. bulgaricus biocatalysts (1:1) and free ones were added in milk for the production of probiotic yogurt. The immobilized biocatalysts were either removed when the pH reached the value 4.6 or were maintained in yogurts for 30 days of storage at 4oC. All produced yogurts showed good physicochemical, organoleptic, volatile and microbiological characteristics, with complete absence of pathogenic microorganisms during their storage at 4 °C for 30 days. Moreover, all yogurts showed high survival rates of immobilized and free L. casei cells (>107 cfu/g) during 30 days of storage (4oC) and so they were characterized as probiotics. Thirdly, probiotic sour milk was produced by incorporation of free and/or immobilized L. casei cells on wheat bran and delignified wheat bran. Each immobilized biocatalyst was either maintained in sour milk for 30 storage days at 4oC or was removed when the pH reached 4.5. All sour milk products were characterized as probiotics (>107 CFU/g) and showed good physicochemical, organoleptic, volatile and microbiological characteristics during 30 days of storage (4 °C). Finally, continuous production of probiotic yogurt and probiotic sour milk was assessed in a 1.5 L bioreactor with milk supplied at a flow rate of 1 L/hour. For continuous yogurt production, L. casei and L. bulgaricus were separately immobilized on delignified wheat bran, freeze dried and used at a ratio 1:1. The system was monitored regardinh pH during passage of 5 liters of milk at 40oC. At the end of each operation hour, 1 liter of effluent milk was received in a sterile glass container and was left for coagulation at 40oC until pH 4.6. Totally 5 parts (1 liter each) of effluent milk were received separately. After passage of this amount of milk no viable L. bulgaricus cells were detected. The number and the concentration of volatile by-products decreased in yogurts as the received volume of effluent milk increased. The products showed good physicochemical, organoleptic and microbiological characteristics during their storage at 4 °C for 30 days. Moreover, all yogurts showed high survival rates L. casei cells (>107 cfu/g) and were characterized as probiotics. For continuous sour milk production, L. casei cells were immobilized on delignified wheat bran and freeze dried. The freeze dried immobilized biocatalyst was introduced in the bioreactor and was used to ferment in total 10 liters of milk. The system was monitored regarding pH during passage of 10 L of milk at 37oC. At the end of each operation hour, 1 liter of effluent milk was received in a sterile glass container and remained for coagulation at 37oC until pH 4.5. Totally 10 parts of effluent milk were received separately. The products showed good physicochemical, organoleptic and microbiological characteristics during their storage at 4 °C for 30 days. The number and the concentration of volatile by-products of sour milk decreased with time in the milk effluents. Moreover, all products showed high survival rates of L. casei cells (>107 cfu/g) and so they were characterized as probiotics. In general, the continuous production of probiotic yoghurt and sour milk yielded promising results for industrial application of this technology while use of whey as a growth and immobilization substrate can result in high quality fermented dairy products with lower cost.