Francesca Patrignani

Antimicrobial Efficacy of Citron Essential Oil on Spoilage and Pathogenic Microorganisms in Fruit-Based Salads

The aim of this study was the evaluation of the effects of pure citral and citron essential oil on microbial spoilage and growth and survival of pathogenic microorganisms during storage. They were added in the syrup of industrial ready-to-eat fruit salads stored at 9 degrees C. Both citral (25 to 125 ppm) and citron essential oil (300, 600, 900 ppm) were able to prolong the microbial shelf life of the fruit-based salads. The essential oil gave excellent results, avoiding the undesirable effects attributable to the cytotoxicity of citral. Citron essential oil doubled the time needed for the wild microflora to reach concentrations able to produce a perceivable spoilage in condition of thermal abuse (9 degrees C). The same essential oil had reduced effects on the survival of Gram-negative species Salmonella Enteritidis and Escherichia coli, but showed a strong inhibition toward the Gram-positive pathogen Listeria monocytogenes.

Probiotic Crescenza Cheese Containing Lactobacillus casei and Lactobacillus acidophilus Manufactured with High-Pressure Homogenized Milk

High-pressure homogenization (HPH) is one of the most promising alternatives to traditional thermal treatment of food preservation and diversification. Its effectiveness on the deactivation of pathogenic and spoilage microorganisms in model systems and real food is well documented. To evaluate the potential of milk treated by HPH for the production of Crescenza cheese with commercial probiotic lactobacilli added, 4 types of cheeses were made: HPH (from HPH-treated milk), P (from pasteurized milk), HPH-P (HPH-treated milk plus probiotics), and P-P (pasteurized milk plus probiotics) cheeses. A strain of Streptococcus thermophilus was used as starter culture for cheese production. Compositional, microbiological, physicochemical, and organoleptic analyses were carried out at 1, 5, 8, and 12 d of refrigerated storage (4 degrees C). According to results obtained, no significant differences among the 4 cheese types were observed for gross composition (protein, fat, moisture) and pH. Differently, the HPH treatment of milk increased the cheese yield about 1% and positively affected the viability during the refrigerated storage of the probiotic bacteria. In fact, after 12 d of storage, the Lactobacillus paracasei A13 cell loads were 8 log cfu/ g, whereas Lactobacillus acidophilus H5 exhibited, in P-P cheese, a cell load decrease of about 1 log cfu/g with respect to the HPH-P cheese. The hyperbaric treatment had a significant positive effect on free fatty acids release and cheese proteolysis. Also, probiotic cultures affected proteolytic and lipolytic cheese patterns. No significant differences were found for the sensory descriptors salty and creamy among HPH and P cheeses as well as for acid, piquant, sweet, milky, salty, creamy, and overall acceptance among HPH, HPH-P, and P-P Crescenza cheeses.

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.

Antimicrobial Activity of Aroma Compounds against Saccharomyces cerevisiae and Improvement of Microbiological Stability of Soft Drinks as Assessed by Logistic Regression

ABSTRACT The combined effects of a mild heat treatment (55°C) and the presence of three aroma compounds [citron essential oil, citral, and (E)-2-hexenal] on the spoilage of noncarbonated beverages inoculated with different amounts of a Saccharomyces cerevisiae strain were evaluated. The results, expressed as growth/no growth, were elaborated using a logistic regression in order to assess the probability of beverage spoilage as a function of thermal treatment length, concentration of flavoring agents, and yeast inoculum. The logit models obtained for the three substances were extremely precise. The thermal treatment alone, even if prolonged for 20 min, was not able to prevent yeast growth. However, the presence of increasing concentrations of aroma compounds improved the stability of the products. The inhibiting effect of the compounds was enhanced by a prolonged thermal treatment. In fact, it influenced the vapor pressure of the molecules, which can easily interact within microbial membranes when they are in gaseous form. (E)-2-Hexenal showed a threshold level, related to initial inoculum and thermal treatment length, over which yeast growth was rapidly inhibited. Concentrations over 100 ppm of citral and thermal treatment longer than 16 min allowed a 90% probability of stability for bottles inoculated with 105 CFU/bottle. Citron gave the most interesting responses: beverages with 500 ppm of essential oil needed only 3 min of treatment to prevent yeast growth. In this framework, the logistic regression proved to be an important tool to study alternative hurdle strategies for the stabilization of noncarbonated beverages.

Role of surface-inoculated Debaryomyces hansenii and Yarrowia lipolytica strains in dried fermented sausage manufacture. Part 1: Evaluation of their effects on microbial evolution, lipolytic and proteolytic patterns.

The aim of this work was to study the effects of Debaryomyces hansenii and Yarrowia lipolytica strains, used with lactic acid starter cultures (Lactobacillus plantarum), on the manufacture of dried fermented sausages to understand their role on sausage microbial evolution, lipolytic and proteolytic patterns. The inoculation of the yeast strains did not markedly affect the sausages microbial flora. The sausages with the yeast strains showed more marked and earlier water activity (a(w)) reductions. Moreover, the surface inoculation of the yeast strains resulted, at the end of ripening, in more pronounced proteolysis and lipolysis. The lipolytic patterns of the products were affected not only by the yeast strain but also by the level of mincing of the meat mixture used.

Lactic acid bacteria and natural antimicrobials to improve the safety and shelf-life of minimally processed sliced apples and lamb's lettuce

Outbreaks of food-borne disease associated with the consumption of fresh and minimally processed fruits and vegetables have increased dramatically over the last few years. Traditional chemical sanitizers are unable to completely eradicate or kill the microorganisms on fresh produce. These conditions have stimulated research to alternative methods for increasing food safety. The use of protective cultures, particularly lactic acid bacteria (LAB), has been proposed for minimally processed products. However, the application of bioprotective cultures has been limited at the industrial level. From this perspective, the main aims of this study were to select LAB from minimally processed fruits and vegetables to be used as biocontrol agents and then to evaluate the effects of the selected strains, alone or in combination with natural antimicrobials (2-(E)-hexenal/hexanal, 2-(E)-hexenal/citral for apples and thyme for lambs lettuce), on the shelf-life and safety characteristics of minimally processed apples and lambs lettuce. The results indicated that applying the Lactobacillus plantarum strains CIT3 and V7B3 to apples and lettuce, respectively, increased both the safety and shelf-life. Moreover, combining the selected strains with natural antimicrobials produced a further increase in the shelf-life of these products without detrimental effects on the organoleptic qualities.

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.

Two 2[5H]-Furanones as Possible Signaling Molecules in Lactobacillus helveticus

ABSTRACT Two 2[5H]-furanones, in association with medium-chain fatty acids, were released in whey by Lactobacillus helveticus exposed to oxidative and heat stresses. This species plays an important role in cheese technology, particularly for Swiss-type cheeses and Grana cheese. Moreover, it significantly contributes to cheese ripening by means of an early autolysis and the release of enzymes during processing. Experimental evidence of the involvement of the two 2[5H]-furanones, detected by a gas chromatography-mass spectrometry/solid-phase microextraction technique, in the autolysis phenomenon has been obtained. Zymograms performed by using renaturing sodium dodecyl sulfate-polyacrylamide gels were used to detect the bioactivity of the supernatants containing the two furanones on fresh cells of the same strain. In addition to bands corresponding to known autolysins, new autolysins were detected concomitant with the exposure of Lactobacillus helveticus to the supernatants, which can be regarded as conditioned media (CM), and to a commercial furanone, 5-ethyl-3-hydroxy-4-methyl-2[5H]-furanone (HEMFi), having spectral data similar to those of the newly described 2[5H]-furanones. Morphological changes were observed when fresh cells were exposed to CM containing the two 2[5H]-furanones and HEMFi. The two furanones produced by Lactobacillus helveticus, which met a number of criteria to be included in cell-cell signaling molecules, have a presumptive molecular mass lower than those of already known 3[2H]-furanones having an autolytic activity and being produced by gram-negative bacteria. Moreover, they present a different chemical structure with respect to the furanones already identified as products of Lactococcus lactis subsp. cremoris or to those identified in some cheeses with Lactobacillus helveticus as a starter culture.

Effect of high pressure homogenisation of milk on cheese yield and microbiology, lipolysis and proteolysis during ripening of Caciotta cheese

The principal aim of this work was to compare Caciotta cheeses obtained from cow milk previously subjected to high pressure homogenisation (HPH) at 100 MPa with those produced from raw (R) or heat-treated (P) cow milk. HPH had both direct and indirect effects on cheese characteristics and their evolution during ripening. In particular, HPH treatment of milk induced a significant increase of the cheese yield; moreover, it affected the microbial ecology of both curd and cheese. Compared with the thermal treatment, the HPH treatment resulted in a decrease of about one log cfu/g of yeast and lactobacilli cell loads of the curd. The initial milk treatment also affected the evolution over time and the levels attained at the end of ripening of all the microbial groups studied. In fact, lactobacilli, microstaphylococci and yeast cell loads remained at lower levels in the cheeses obtained from HPH milk with respect to the other cheese types over the whole ripening period. Moreover, HPH of milk induced marked and extensive lipolysis. Cheeses from HPH milk showed the presence of high amounts of free fatty acids immediately after brining. The electrophoretic patterns of the different cheese types showed that Caciotta made from HPH-treated milk was characterized by a more extensive and faster proteolysis as well as a significant modification of its volatile molecule profile. The results obtained and the sensory analysis indicated that HPH treatment of milk was able to differentiate Caciotta cheese or to modify its ripening patterns.

Resistance of two temperate Lactobacillus paracasei bacteriophages to high pressure homogenization, thermal treatments and chemical biocides of industrial application

Temperate bacteriophages ф iLp84 and ф iLp1308, previously isolated from mitomycin C-induction of Lactobacillus paracasei strains 84 and CNRZ1308, respectively, were tested for their resistance to several physical and chemical treatments applied in dairy industry. Long-term survival at 4 °C, -20 °C and -80 °C, resistance to either thermal treatments of 63 °C, 72 °C and 90 °C, high pressure homogenization (HPH, 100 MPa) or classic (ethanol, sodium hypochlorite and peracetic acid) and new commercial sanitizers, namely A (quaternary ammonium chloride), B (hydrogen peroxide, peracetic acid and peroctanoic acid), C (alkaline chloride foam), D (p-toluensulfonchloroamide, sodium salt) and E (ethoxylated nonylphenol and phosphoric acid), were determined. Phages were almost completely inactivated after eight months of storage at 25 °C, but viability was not affected at 4 °C, -20 °C or -80 °C. Both phages tolerated well HPH treatments. Phage iLp1308 showed higher thermal resistance than ф iLp84, but neither resisted 90 °C for 2 min. Best chemical inactivation was accomplished using peracetic acid or biocides A, C and E, whereas biocides B and D were completely ineffective. These results help to improve selection of chemical agents and physical treatments to effectively fight against phage infections in dairy plants.