Barbara Dal Bello

Technological characterization of bacteriocin producing Lactococcus lactis strains employed to control Listeria monocytogenes in Cottage cheese

In recent years, there has been a particular focus on the application of antimicrobial compounds produced by lactic acid bacteria (LAB) as natural preservatives to control the growth of spoilage and pathogenic bacteria in food. Bacteriocins are antimicrobial peptides which can be added to foods in concentrated forms as food preservatives, e.g. additives, or they can be produced in situ by starters or protective cultures. In this study, twenty Lactococcus lactis bacteriocin producers previously isolated from Italian fermented foods were subjected to a variety of physical and biochemical tests in order to identify those with the greatest potential as starter cultures in cheese production. Of these, four strains isolated from cheese (one nisin Z producer, one nisin A producer and two lacticin 481 producers) which fulfilled the desired technological criteria were assessed for their ability to control Listeria monocytogenes. The subsequent application of these bacteriocinogenic strains as starter cultures in Cottage cheese established that the nisin A producing Lact. lactis 40FEL3, and to a lesser extent the lacticin 481 producers 32FL1 and 32FL3, successfully controlled the growth of the pathogen. This is the first study to directly compare the ability of nisin A, nisin Z and lacticin 481 producing strains to control listerial growth during the manufacture and storage of Cottage cheese.

Microbiota of Minas cheese as influenced by the nisin producer Lactococcus lactis subsp. lactis GLc05.

Minas cheese is a popular dairy product in Brazil that is traditionally produced using raw or pasteurized cow milk. This study proposed an alternative production of Minas cheese using raw goat milk added of a nisin producer Lactococcus lactis subsp. lactis GLc05. An in situ investigation was carried on to evaluate the interactions between the L. lactis subsp. lactis GLc05 and the autochthonous microbiota of a Minas cheese during the ripening; production of biogenic amines (BAs) was assessed as a safety aspect. Minas cheese was produced in two treatments (A, by adding L. lactis subsp. lactis GLc05, and B, without adding this strain), in three independent repetitions (R1, R2, and R3). Culture dependent (direct plating) and independent (rep-PCR and PCR-DGGE) methods were employed to characterize the microbiota and to assess the possible interferences caused by L. lactis subsp. lactis GLc05. BA amounts were measured using HPLC. A significant decrease in coagulase-positive cocci was observed in the cheeses produced by adding L. lactis subsp. lactis GLc05 (cheese A). The rep-PCR and PCR-DGGE highlighted the differences in the microbiota of both cheeses, separating them into two different clusters. Lactococcus sp. was found as the main microorganism in both cheeses, and the microbiota of cheese A presented a higher number of species. High concentrations of tyramine were found in both cheeses and, at specific ripening times, the BA amounts in cheese B were significantly higher than in cheese A (p<0.05). The interaction of nisin producer L. lactis subsp. lactis GLc05 was demonstrated in situ, by demonstration of its influence in the complex microbiota naturally present in a raw goat milk cheese and by controlling the growth of coagulase-positive cocci. L. lactis subsp. lactis GLc05 influenced also the production of BA determining that their amounts in the cheeses were maintained at acceptable levels for human consumption.

Chemical, mechanical and sensory monitoring of hot air- and infrared-roasted hazelnuts (Corylus avellana L.) during nine months of storage

Roasted hazelnuts can be consumed as whole nuts, or as an ingredient in the confectionary and bakery industries and are highly appreciated for their typical taste, aroma and crunchy texture. In this work, two hazelnut types (TGT, Ordu) from two harvests were roasted using two different systems (hot air, infrared) at different time/temperature combinations, and the evolution of oxidative stability, the total phenolic content (TPC), the antioxidant capacity, the mechanical and acoustic properties and the sensory perception were determined during storage. The results showed that the oxidative stability was increased by roasting hazelnuts at 120°C for 40min with hot air system. Similar overall trends were not found for the TPC, the antioxidant capacity and the mechanical-acoustic properties. However, for the maintenance of high antioxidant activity, a storage time of 6months at 4°C is recommended. The two roasting systems gave hazelnuts with significant sensory differences only at high roasting temperature.

Effect of nisin‐producing Lactococcus lactis starter cultures on the inhibition of two pathogens in ripened cheeses

The effect of Lactococcus lactis nisin-producing strains, isolated from Italian fermented foods, onthe survival of two foodborne pathogens namely Listeria monocytogenes and Staphylococcus aureuswas investigated in experimental cheese production. One of the three Lactobacillus lactis nisin inn-oculated as starters, Lactobacillus lactis 41FL1 lowered S. aureus count by 1.73 log colony-formingunits (cfu)/g within the first 3 days, reaching the highest reduction, 3.54 log cfu/g, by the end ofripening period of 60 days. There was no effect on L. monocytogenes. The application of L. lactis41FL1 as bioprotective culture in controlling S. aureus shows considerable promise.Keywords Lactococcus lactis, nisin, Staphylococcus aureus, Listeria monocytogenes, Cheese.INTRODUCTIONLactic acid bacteria (LAB) are widely used forthe fermentation and preservation of a widerange of milk, meat and vegetable foods.Among LAB strains, Lactococcus lactis isextensively used as starter culture in the dairyindustry, and the potential applications of thesestrains in food production are well documented.In particular, in recent years, great interest wasfocused on the possible use of certain productsof their metabolism, called bacteriocins, aspotential biopreservatives in foods (O’Sullivanet al. 2002).Bacteriocins are proteinaceous antimicrobialcompounds ribosomially synthesised by bacteriaand able to inhibit a high number of potentialpathogens among which Listeria monocytogenesand Staphylococcus aureus (Cotter et al. 2005).The current technologies employed to inacti-vate bacterial pathogens in foods are not alwaysefficient and often represent particular treatmentsthat may modify the fisical and chemical proper-ties of the food products. Therefore, newapproaches to combat pathogenic and spoilagemicroorganisms are needed. In the last fewyears, bacteriocins from LAB have been thor-oughly characterised and tested in food systemsas new food preservatives (Stiles 1996).Although many bacteriocins have been charac-terised, two of the most widely used in foodindustry as biopreservative are nisin (Class I,lantibiotic) and pediocin (Class II). Nisin is thebacteriocin with the longest history of safe usein food industry. It has been shown to be effec-tive for the microbial control in a number ofdairy products and also widely assessed incheese manufacturing (Ross et al. 2002). Inmost of cases, the bacteriocin is incorporatedinto the product as a dried concentrated powder(O’Sullivan et al. 2002), but currently, the useof nisin-producing starter or costarter culturesseems to be an alternative way of incorporatingthe bacteriocin (e.g. cheesemaking process)(Sobrino-Lopez and Marton-Belloso 2008).Among the pathogenic bacteria potentiallyassociated with dairy foods, S. aureus andL. monocytogenes are the cause of numerous

Static Hot Air and Infrared Rays Roasting are Efficient Methods for Aflatoxin Decontamination on Hazelnuts

Aflatoxins are a group of secondary metabolites produced by members of Aspergillus Section Flavi that are dangerous to humans and animals. Nuts can be potentially contaminated with aflatoxins, often over the legal threshold. Food processes, including roasting, may have different effects on mycotoxins, and high temperatures have proven to be very effective in the reduction of mycotoxins. In this work, two different roasting methods—traditional static hot air roasting and infra-red rays roasting—were applied and compared for the detoxification of hazelnuts from Italy and Turkey. At the temperature of 140 °C for 40 min of exposure, detoxification was effective for both roasting techniques. Residual aflatoxins after infra-red rays treatments were lower compared to static hot air roasting. On Italian hazelnuts, residual aflatoxins were lower than 5%, while for Turkish hazelnuts they were lower than 15% after 40 min of exposure to an infra-red rays roaster. After roasting, the perisperm was detached from the nuts and analyzed for aflatoxin contents. Residual aflatoxins in the perisperm ranged from 80% up to 100%. After roasting, the lipid profile and the nutritional quality of hazelnuts were not affected. Fatty acid methyl esters analyses showed a similar composition for Italian and Turkish hazelnuts.

Technological properties and biogenic amines production by bacteriocinogenic lactococci and enterococci strains isolated from raw goat's milk

Technological properties and biogenic amine production were analyzed in 56 bacteriocinogenic lactococci and enterococci strains isolated from raw goats milk. Fifteen lactococci strains were able to reduce milk pH to 5.3 or lower after 6 h, while enterococci strains were initially slow in producing acids. Lactococcus lactis subsp. lactis GLc06 and three strains of Enterococcus faecalis (GEn20, GEn22, and GEn23) presented high proteolytic activity. L. lactis subsp. lactis GLc06 and E. faecalis GEn22 also showed a high percentage of autolysis after only 4 h, reaching 71.11 and 97.67%, respectively, after 24 h. No strain was able to secrete exopolysaccharides, and L. lactis subsp. lactis GLc22 and 25 of the Enterococcus strains were able to produce diacetyl. L. lactis subsp. lactis GLc05 and 23 of the Enterococcus strains presented a high tolerance to NaCl at 10% (wt/vol). Regarding biogenic amine production, 12 strains (5 lactococci and 7 enterococci) were capable of forming tyramine and 4 strains (1 lactococcus and 3 enterococci) were capable of forming 2-phenylethylamine, but in very low amounts. GLc06 presented great acidifying, proteolytic, and autolytic activities, and GLc05 was capable of growing at high NaCl concentrations (10%, wt/vol), possessing medium autolytic and proteolytic activities. Some enterococci strains produced diacetyl and high autolytic and extracellular proteolytic activities and also presented resistance to high NaCl concentrations. The interesting technological properties presented by some bacteriocinogenic strains can justify their use by the dairy industry, with the aim of ensuring both safety due to bacteriocin production and technological transformations in fermented products.

Fresh cheese as a vehicle for polyunsaturated fatty acids integration: effect on physico-chemical, microbiological and sensory characteristics

Abstract Five different vegetable oils were used in the production of fresh cheese to increase the concentration of polyunsaturated fatty acids (PUFAs), particularly α-linolenic acid (ALA), the most important omega-3 fatty acid of vegetable origin. Physico-chemical and microbiological characteristics of functionalized cheeses were evaluated after 1 and 3 days of ripening at 4 °C while the consumer appreciation was evaluated in the final product at 3 days of ripening. After 3 days, the cheeses with Camelina sativa and Echium plantagineum oils added exhibited the highest retention of PUFAs (mostly ALA) compared to those with flaxseed, raspberry and blackcurrant oils. The addition of oil showed little effects on physico-chemical characteristics and also consumers’ evaluation highlighted that all of the fresh cheeses were considered acceptable although those with flaxseed and raspberry oils were the most appreciated.