Pasquale M. Falcone

A Study on the Antimicrobial Activity of Thymol Intended as a Natural Preservative

A quantitative investigation on the inhibitory activity of thymol against some microorganisms that could represent a potential spoilage risk both in acid and mild thermally treated foods is presented in this work. In order to assess potential biostatic or biocidal activity of thymol, both the growth kinetics and dose-response profiles were obtained and analyzed. A suitable macrodilution methodology based on a turbidimetric technique was adopted to produce inhibitory data used for characterizing microbial susceptibility against thymol at sub-MIC levels. Microbial growth was monitored through absorbance measurements at 420 nm as a function of contact time with the active compound. Moreover, for each tested microorganism, the noninhibitory concentration (NIC) and the MIC were quantified. Results prove that thymol can exert a significant antimicrobial effect on each phase of the growth cycle. The microbial susceptibility and resistance were found to be nonlinearly dose related. It is worth noting that significant biostatic effects were observed at sub-MIC levels.

Molecular size and molecular size distribution affecting traditional balsamic vinegar aging.

A first attempt at a semiquantitative study of molecular weight (MW) and molecular weight distribution (MWD) in cooked grape must and traditional balsamic vinegar (TBV) with increasing well-defined age was performed by high-performance liquid size exclusion chromatography (SEC) using dual detection, that is, differential refractive index (DRI) and absorbance (UV-vis) based detectors. With this aim, MW and MWD, including number- and weight-average MW and polydispersity, were determined with respect to a secondary standard and then analyzed. All investigated vinegar samples were recognized as compositionally and structurally heterogeneous blends of copolymers (melanoidins) spreading over a wide range of molecular sizes: the relative MW ranged from 2 to >2000 kDa. The extent of the polymerization reactions was in agreement with the TBV browning kinetics. MWD parameters varied asymptotically toward either upper or lower limits during aging, reflecting a nonequilibrium status of the balance between polymerization and depolymerization reactions in TBV. MWD parameters were proposed as potential aging markers of TBV.

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.

Use of entrapped microorganisms as biological oxygen scavengers in food packaging applications

Abstract In this work a new method is proposed to produce oxygen-scavenger films using aerobic microorganisms as the “active compound”. The manufacturing cycle of the investigated oxygen-scavenger film was optimized both to prolong the microorganisms viability during storage and to improve the efficiency of the film to remove oxygen from the package headspace. It was found that it is possible to store the desiccated film over a period of 20 days without monitoring any appreciable decrease of microorganism viability. It was also pointed out that the highest respiratory efficiency of the proposed active film is obtained by entrapping the microorganisms into polyvinyl alcohol, and by using the active film as a coating for a high humidity food.

Sugar conversion induced by the application of heat to grape must.

Two lots of the grape Trebbiano cultivar were harvested from the same vineyard 15 days apart, and their musts were cooked in an open stainless steel pan directly heated by fire; the kinetics of formation or disappearance of key constituents was then monitored for at least 16 h. From an engineering standpoint, the vessel behaved like a nonisothermal batch reactor in which the volume of the grape must necessarily decreased while its composition changed profoundly as a result of chemical reactions. Brix, total titratable acids, acetic acid, malic acid, lactic acid (d and l), pH, water activity, 5-HMF, and phenolic and radical-scavenging compounds were proposed as markers of the extent of cooking for which water vaporization and sugar degradation were identified as the two main driving factors. Acid-catalyzed dehydration was hypothesized as the predominant mechanism for sugar degradation, assuming a direct role of water vaporization; however, contributions of Maillard degradation pathways and other parallel reversible reactions were also hypothesized. Fractional conversion of 5-HMF and radical-scavenging compounds were proposed as quantitative markers for the extent of sugar degradation at, respectively, the early and advanced stages of cooking. Selectivity indices were also proposed as a performance criterion to design cooking processes in relation to sugar degradation.

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.

The study of acidifying blanching of pickled “Cicorino” leaves using Response Surface Methodology

Abstract Response Surface Methodology was applied to investigate variables such as concentration of citric acid in the blanching solution, time of treatment and number of recycles of the blanching solution, which affect the acidifying blanching of pickled “Cicorino” leaves. A Central Composite Design was developed to model the variables. Results showed that the obtained models were able to provide a good estimate of the effects of individual and interactive factors on the final pH of “Cicorino”. Among the considered factors, citric acid concentration is the main variable affecting sample pH value. The number of recycles did not affect in a negative way pH value providing an extension of the blanching time.

Biotechnological production of cellulose by acetic acid bacteria: current state and perspectives

Bacterial cellulose is an attractive biopolymer for a number of applications including food, biomedical, cosmetics, and engineering fields. In addition to renewability and biodegradability, its unique structure and properties such as chemical purity, nanoscale fibrous 3D network, high water-holding capacity, high degree of polymerization, high crystallinity index, light transparency, biocompatibility, and mechanical features offer several advantages when it is used as native polymer or in composite materials. Structure and properties play a functional role in both the biofilm life cycle and biotechnological applications. Among all the cellulose-producing bacteria, acetic acid bacteria of the Komagataeibacter xylinus species play the most important role because they are considered the highest producers. Bacterial cellulose from acetic acid bacteria is widely investigated as native and modified biopolymer in functionalized materials, as well as in terms of differences arising from the static or submerged production system. In this paper, the huge amount of knowledge on basic and applied aspects of bacterial cellulose is reviewed to the aim to provide a comprehensive viewpoint on the intriguing interplay between the biological machinery of synthesis, the native structure, and the factors determining its nanostructure and applications. Since in acetic acid bacteria biofilm and cellulose production are two main phenotypes with industrial impact, new insights into biofilm production are provided.