Potentialities of high-pressure homogenization to inactivate Zygosaccharomyces bailii in fruit juices.

UNLABELLED: This experimental work was aimed to evaluate the effects of repeated high-pressure homogenization (HPH) treatments at 100 MPa on the inactivation and regrowth of Zygosaccharomyces bailii inoculated in apricot and carrot juices. Thus, the spoilage yeast was inoculated in both the juices at level of about 5 log CFU/g and the 2 systems were treated with a lab-scale Panda homogenizer for 8 passes at 100 MPa. Microbiological and chemico-physical analyses were performed immediately after the treatment and during the juice storage at room temperature. Microbial data highlighted that yeast inactivation increased with the number of passes applied. Eight passes at 100 MPa allowed yeast inactivation higher than 2.5 log CFU/mL regardless of the juice considered. On the contrary, the juice type affected the yeast fate (growth or death) over the storage at 25 degrees C. In fact, Z. bailii was able to attain the spoilage threshold (6 log CFU/mL) in apricot juice, although with growth kinetics dependent of the survivor levels after HPH treatment. In carrot juice this microorganism was unable to recover over the storage in the most severely treated samples. The HPH treatment had a significant effect on apricot juice pH and viscosity, while no significant effect was observed in carrot juice. The viscosity measurements showed that the application of one pass at 100 MPa resulted in the triplication of apricot viscosity index. No further significant viscosity increase (P > 0.05) was observed increasing the number of passes at 100 MPa. PRACTICAL APPLICATION: The results obtained in the present study and the proposed technology could be exploited by the industries of the beverage sector to increase the shelf life of these kinds of products. Moreover, from a technological point of view, the increase of viscosity, following the high-pressure homogenization treatment, represents a tool to expand the product gamma without the use of gelling additives or thermal treatments, which are detrimental for the sensorial and nutritional properties of this kind of products.

Effect of high pressure homogenization on Saccharomyces cerevisiae inactivation and physico-chemical features in apricot and carrot juices.

This experimental work aimed to evaluate the potential of high pressure homogenization (HPH) to inactivate Saccharomyces cerevisiae 635 inoculated both in apricot and carrot juices. The sensitivity of the yeast was evaluated both in relation to its initial inoculum level (about 3.0 and 6.0 Log(10) cfu/ml) and number of passes applied at 100 MPa. Moreover, the effects of repeated pressure treatments at 100 MPa were evaluated for pH, water activity and viscosity of carrot and apricot juices. Data obtained showed that repeated high pressure homogenization passes at 100 MPa allowed a significant inactivation of the spoilage yeast inoculated in both juices. However, as expected, the inactivation of the considered strain was greatly affected by the food matrix. In fact, a higher viability loss of S. cerevisiae 635 was observed in carrot juice than in apricot juice. Concerning the recovery, data obtained showed that the decrease of the inoculum level to 3.0 Log(10) cfu/ml prevented (at least for 6 days) cell proliferation in the samples of apricot and carrot juices treated with more than four and seven passes, respectively. Also the refrigeration of the treated samples prevented cell recovery and, in some cases, induced a further decrease in cell viability also in the samples inoculated with 6.0 Log(10) cfu/ml allowing a further increase in the juice shelf-life. An interesting and promising result was the enhanced viscosity of apricot juices treated up to five passes at 100 MPa.