Matteo Alessandro Del Nobile

Food applications of natural antimicrobial compounds

In agreement with the current trend of giving value to natural and renewable resources, the use of natural antimicrobial compounds, particularly in food and biomedical applications, becomes very frequent. The direct addition of natural compounds to food is the most common method of application, even if numerous efforts have been made to find alternative solutions to the aim of avoiding undesirable inactivation. Dipping, spraying, and coating treatment of food with active solutions are currently applied to product prior to packaging as valid options. The aim of the current work is to give an overview on the use of natural compounds in food sector. In particular, the review will gather numerous case-studies of meat, fish, dairy products, minimally processed fruit and vegetables, and cereal-based products where these compounds found application.

Shelf life of ready to use peeled shrimps as affected by thymol essential oil and modified atmosphere packaging.

In this work the influence of different packaging strategies on the shelf life of ready to use peeled shrimps was investigated. First, the effectiveness of the coating (Coat) and the active coating loaded with different concentrations of thymol (Coat-500, Coat-1000, and Coat-1500) on the quality loss of the investigated food product packaged in air was addressed; afterwards, the thymol concentration that had shown the best performance was used in combination with MAP (5% O(2); 95% CO(2)). Microbial cell load of main spoilage microorganisms, pH and sensorial quality were monitored during the refrigerated storage. Results of the first step suggested that the sole coating did not affect the microbial growth. A slight antimicrobial effect was obtained when the coating was loaded with thymol and a concentration dependence was also observed. Moreover, the active coating was effective in minimizing the sensory quality loss of the investigated product, it was particularly true at the lowest thymol concentration. In the second step, the thymol concentration (1000 ppm) that showed the strike balance between microbial and sensorial quality was chosen in combination with MAP. As expected, MAP significantly affected the growth of the mesophilic bacteria. In particular, a cell load reduction of about 2 log cycle for the samples under MAP respect to that in air was obtained. Moreover, the MAP packaging inhibited the growth of the Pseudomonas spp. and hydrogen sulphide-producing bacteria. The MAP alone was not able to improve the shelf life of the uncoated samples. In fact, no significant difference between the control samples packaged in air and MAP was observed. Whilst, the use of coating under MAP condition prolonged the shelf life of about 6 days with respect to the same samples packaged in air. Moreover, when the MAP was used in combination with thymol, a further shelf life prolongation with respect to the samples packaged in air was observed. In particular, a shelf life of about 14 days for the active coating under MAP compared to the same samples in air (5 days) was obtained.

New strategies for reducing the pork back-fat content in typical Italian salami

In this work the possibility to substitute pork backfat with extra virgin olive oil (EVOO), adsorbed on whey protein-based crumb or white bread crumb, in typical Italian salami is addressed. Five types of salami were manufactured, under the usual commercial conditions, by replacing 0 (Control), 60% and 100% of pork backfat with whey protein-based crumb (WP60-WP100) and white pan bread (PB60-PB100), respectively, soaked in EVOO. Results highlighted that pH, weight loss, colour parameters and microbial counts did not show statistically significant differences between the Control and the modified salami. On the other hand, malonaldehyde was slightly lower in PB100, PB60, WP100 and WP60, compared to the Control. Chemical composition was significantly affected by formulations. Modified salami presented a better fatty acid profile showing lower saturated and higher monounsaturated fatty acids than control. Furthermore in all modified salami atherogenic and thrombogenic indices displayed the lowest values. The Control showed the highest values for Warner-Bratzler Shear, hardness, cohesiveness, gumminess and chewiness. Sensory evaluation of WP60 did not show significant differences compared to the Control, whereas PB100 and WP100 were unacceptable for taste.

Imaging Techniques for the Study of Food Microstructure: A Review

Publisher Summary This chapter presents a review on imaging techniques for the study of food microstructure. The quality of a food product is related to its sensorial—shape, size, color, and mechanical (texture) characteristics. These features are strongly affected by the food structural organization that can be studied at molecular, microscopic, and macroscopic levels. In particular, the microstructure and interactions of components, such as protein, starch, and fat, determine the texture of a food that could be defined as the ‘‘external manifestation of this structure.’’ Because the microstructure affects food sensorial properties, foods having a similar microstructure also have a similar behavior. Studies on food microstructure can be performed by means of a large variety of techniques allowing the generation of data in the form of images. With the development of more powerful tools, such as the X-ray-computed tomographic scanners, both 2D and 3D digital images of the food internal structure can be readily acquired with high resolution and contrast and without any sample preparation. These images can be processed by means of the fractal and stereological analysis to quantify a number of structural elements. Fractal analysis allows the investigation of the fractal geometry in both 2D and 3D digital images.

Antimicrobial Effectiveness of Lysozyme Immobilized on Polyvinylalcohol-Based Film against Alicyclobacillus acidoterrestris

In this study, the effectiveness of an active polyvinylalcohol-based film against Alicyclobacillus acidoterrestris was assessed. The active film was fabricated by immobilizing an active compound on the surface of a polymeric matrix and then tested by putting the film in contact with a medium that had been inoculated with microbial cells. Microbiological tests showed that the film was antimicrobial against both a single strain and a culture cocktail of A. acidoterrestris, at 44 degrees C. By monitoring the viable cell concentration under three different packaging conditions, it was possible to demonstrate that the active film was equally effective against both the single strain and the culture cocktail and that it maintained this efficacy at various medium volumes. The same microbial tests were also conducted on viable spores of the investigated microorganism, inoculated both into a laboratory medium and apple juice. The results indicate that these viable spores were better inhibited than cells by the active film in both investigated media.

Shelf life of reduced pork back-fat content sausages as affected by antimicrobial compounds and modified atmosphere packaging

The combined use of antimicrobial compounds and modified atmosphere packaging (MAP) on shelf life of reduced pork back-fat content sausages was investigated in this study. First, a pre-screening of different antimicrobial compounds and MAP was addressed. In particular, the consumer test was used as a tool to select the most pleasant antimicrobial compounds, whereas both sausage color and cell load of main spoilage microorganisms were used to choose optimal MAP. Afterwards, antimicrobial compounds (lemon alkott and thymol) and MAP (MAP1: 20% CO(2), 5% O(2), 75% N(2)) that had shown the best performance were used to run the shelf life tests. In order to assess the influence of the variables described beforehand on the shelf life of investigated sausages, the sensorial and microbiological (mesophilic and psychrotrophic bacteria, Enterobacteriaceae, Pseudomonas spp., lactic acid bacteria and coccus-shaped lactic acid bacteria) quality was monitored during storage. Results recorded in this study suggested that Pseudomonas spp. were responsible for sausage unacceptability in all samples, except for thymol and thymol-MAP samples. For these samples, the sensorial quality was the limiting factor while the microbial growth did not limit the shelf life. In particular, for thymol and thymol-MAP samples a shelf life value of more than 5 days with respect to the other samples (2 days) was obtained.

Evaluating In Vitro Antimicrobial Activity of Thymol toward Hygiene-Indicating and Pathogenic Bacteria

Results of a study of the kinetics of bacterial inhibition by thymol in order to develop appropriate applications for the compound in food systems are presented. A modeling-based approach was used to provide a quantitative description of the antimicrobial activity of thymol toward some foodborne pathogens and hygiene-indicating bacteria, which could be postprocessing contaminants of ready-to-eat meat products. The effect of the active compound on the bacterial growth was assessed from growth kinetics curves and dose-response profiles in a wide range of thymol concentrations, i.e., from 50 to 1,000 ppm. Inhibitory data were produced using a macrodilution methodology based on a turbidimetric technique. Microbial response was discussed in terms of Gompertzs parameters as well as in terms of the active concentration of thymol affecting the growth status of microbial suspension (noninhibitory concentration and MIC). Results suggested that thymol can be successfully used as an alternative antimicrobial to increase the lag time as well as to decrease the maximum value of the growth index as reached in the stationary phase of the growth cycle for all investigated bacteria. Due to their high sensitivity to the antimicrobial stress as observed at sub-MIC, it is arguably a potential use of thymol for assurance of food safety and hygiene in combination with other preservative technologies. A quantitative evaluation of the antimicrobial properties of the active compound was performed using a macrodilution methodology based on a turbidimetric technique to produce inhibitory data. Both the growth kinetics and inhibition profile in a wide range of thymol concentrations were obtained for each test bacterium, mathematically modeled, and analyzed. Noninhibitory concentration and MIC were determined to investigate both the microbial sensibility and resistance toward thymol, and Gompertzs parameters were evaluated to assess the microbial response at each phase of growth cycle. The in vitro-obtained results suggested that thymol may be successfully used as a alternative preservative to increase the lag time as well as to decrease the maximum cell load reached in the stationary phase of growth cycle for all investigated bacteria.

Modelling the survival of starter lactic acid bacteria and Bifidobacterium bifidum in single and simultaneous cultures.

The inactivation kinetics at 4 degrees C of Bifidobacterium bifidum, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, cultured alone or consociated in a laboratory medium (modified MRS broth), were modelled through the Weibull model and a second-order polynomial equation. The initial cell number of S. thermophilus and L. delbrueckii subsp. bulgaricus was approximately 6-7log (CFU/ml); the viability loss after 30 days of storage was 2.87 and 1.99log (CFU/l) for L. delbruckii subsp. bulgaricus and S. thermophilus, cultured alone, respectively; whereas the consociation of lactobacilli and streptococci with bifidobacteria reduced viability loss during storage (0.28 and 0.54log CFU/l for lactobacilli and streptococci, respectively). Finally, the consociation of lactobacilli and streptococci with B. bifidum improved their oxygen uptake.

Use of purple durum wheat to produce naturally functional fresh and dry pasta.

In this study, the effects of different milling procedures (roller-milling vs. stone-milling) and pasta processing (fresh vs. dried spaghetti), and cooking on the antioxidant components and sensory properties of purple durum wheat were investigated. Milling and pasta processing were performed using one purple and one conventional non-pigmented durum wheat genotypes, and the end-products were compared with commercial pasta. The results show that the stone milling process preserved more compounds with high health value (total fibre and carotenoids, and in the purple genotype, also anthocyanins) compared to roller-milling. The drying process significantly (p<0.05) reduced the content of anthocyanins (21.42 μg/g vs. 46.32 μg/g) and carotenoids (3.77 μg/g vs. 4.04 μg/g) with respect to the pasteurisation process involved in fresh pasta production. The sensory properties of pasta from the purple genotype did not significantly differ from commercial wholemeal pasta, and its in vitro glycemic index was even lower. Thus, it is possible to consider this genetic material as a good ingredient for the production of functional foods from cereals naturally rich in bioactive compounds.

Effects of different vinification technologies on physical and chemical characteristics of Sauvignon blanc wines.

In order to investigate the effects of cryomaceration and reductive vinification on chemical and physical indices and on antioxidant compounds of Sauvignon blanc wines, four wine-making procedures were applied: traditional white vinification, skin cryomaceration, vinification in a reductive environment, and a combination of the last two procedures. Significant differences were highlighted by both conventional analyses and NMR spectroscopy. The strongest changes were for organic acid concentrations (tartaric, in particular) and phenolic content. Cryomaceration caused a strong precipitation of tartaric acid, which may be desired if grapes have high acidity values. Cryomaceration protected those flavans reactive with vanillin from the action of oxidative enzymes. Vinification in a reductive environment, alone or combined with a cryomaceration step, gave wines with the highest solids content and caused a greater extraction of phenolic compounds from skins compared to traditional winemaking or cryomaceration alone, due to SO(2) solubilisation. Grape oenological expression can be strongly affected by the application of the investigated wine-making procedures.