María Roberta Ansorena

Assessment of lettuce quality during storage at low relative humidity using Global Stability Index methodology

Abstract During postharvest, lettuce is usually exposed to adverse conditions (e.g. low relative humidity) that reduce the vegetable quality. In order to evaluate its shelf life, a great number of quality attributes must be analyzed, which requires careful experimental design, and it is time consuming. In this study, the modified Global Stability Index method was applied to estimate the quality of butter lettuce at low relative humidity during storage discriminating three lettuce zones (internal, middle, and external). The results indicated that the most relevant attributes were: the external zone - relative water content, water content , ascorbic acid, and total mesophilic counts; middle zone - relative water content , water content, total chlorophyll , and ascorbic acid; internal zone - relative water content, bound water, water content, and total mesophilic counts. A mathematical model that takes into account the Global Stability Index and overall visual quality for each lettuce zone was proposed. Moreover, the Weibull distribution was applied to estimate the maximum vegetable storage time which was 5, 4, and 3 days for the internal, middle, and external zone, respectively. When analyzing the effect of storage time for each lettuce zone, all the indices evaluated in the external zone of lettuce presented significant differences (p < 0.05). For both, internal and middle zones, the attributes presented significant differences (p < 0.05), except for water content and total chlorophyll.

Optimization of thermal processing of canned mussels

The design and optimization of thermal processing of solid–liquid food mixtures, such as canned mussels, requires the knowledge of the thermal history at the slowest heating point. In general, this point does not coincide with the geometrical center of the can, and the results show that it is located along the axial axis at a height that depends on the brine content. In this study, a mathematical model for the prediction of the temperature at this point was developed using the discrete transfer function approach. Transfer function coefficients were experimentally obtained, and prediction equations fitted to consider other can dimensions and sampling interval. This model was coupled with an optimization routine in order to search for different retort temperature profiles to maximize a quality index. Both constant retort temperature (CRT) and variable retort temperature (VRT; discrete step-wise and exponential) were considered. In the CRT process, the optimal retort temperature was always between 134 °C and 137 °C, and high values of thiamine retention were achieved. A significant improvement in surface quality index was obtained for optimal VRT profiles compared to optimal CRT. The optimization procedure shown in this study produces results that justify its utilization in the industry.

Optimization of medium components and physicochemical parameters to simultaneously enhance microbial growth and production of lypolitic enzymes by Stenotrophomonas sp.

The optimization of lipase and esterase production (LP and EP) and bacterial growth (BG) of a Stenotrophomonas sp. strain was developed. For this purpose, the effect of five different medium components and three physicochemical parameters were evaluated using a Plackett–Burman statistical design. Among eight variables, stirring speed, pH, and peptone concentration were found to be the most effective factors on the three responses under evaluation. An optimization study applying Box–Behnken response surface methodology was used to study the interactive effects of the three selected variables on LP/EP and microorganism growth. Predicted models were found to be significant with high regression coefficients (90%–99%). By using the desirability function approach, the optimum condition applying simultaneous optimization of the three responses under study resulted to be: stirring speed of 100 rpm, pH of 7.5, and a peptone concentration of 10 g/L, with a desirability value of 0.977. Under these optimal conditions, it is possible to achieve in the optimized medium a 15‐fold increase in esterase productivity, a 117‐fold increase in lipase production, and a 9‐log CFU/mL increase in BG, compared with the basal medium without agitation.

Food Biopackaging Based on Chitosan

Chitin, available from waste products of the shellfish industry (shells of the crab, shrimp, etc.), is one of the most abundant natural polymers in the world, and it is used for the production of chitosan by deacetylation. Chitosan, a cationic polysaccharide, natural, nontoxic, biodegradable, biocompatible, bioadhesive, and available commercially, has been employed in a variety of applications ranging from membrane separation, tissue engineering, wound healing, and dressing to hydro gels formation and biodegradable films for food packaging. It is also a well-known biopolymer for its broad antimicrobial activity against bacteria and fungi. Chitosan possesses high positive charge on NH3 + groups when dissolved in aqueous acidic solution, and therefore it is able to adhere to or aggregate with negatively charged molecules forming three-dimensional networks. Moreover, chitosan acts as stabilizer of hydrocolloids, lipids, and mixtures, promoting emulsion formation and interfacial stabilization, so it is frequently used as emulsifier in film-forming solutions. Due to all these advantageous characteristics added to its excellent film-forming properties and low cost, chitosan has generated enormous interests, and thus the quantity and quality of research using this polymer in the area of packaging have increased steadily in the last few years. Chitosan-based food packaging can be classified as “active” because they include systems capable of inhibiting microorganism action and avoiding loss of food quality. In particular, the antimicrobial packaging is one of the most innovative M.R. Ansorena (*) Food Engineering Group, Chemical Engineering Department, Engineering Faculty, National University of Mar del Plata, Mar del Plata, Argentina e-mail: ransorena@fi.mdp.edu.ar N.E. Marcovich • M. Pereda Ecomaterials, Instituto de Investigaciones en Ciencia y Tecnología de Materiales (INTEMA-CONICET), Mar del Plata, Argentina e-mail: marcovic@fi.mdp.edu.ar; mpereda@fi.mdp.edu.ar # Springer International Publishing AG 2018 L.M.T. Martínez et al. (eds.), Handbook of Ecomaterials, https://doi.org/10.1007/978-3-319-48281-1_68-1 1 and promising active packaging types developed over the last decade. Accordingly, this chapter discusses in detail the latest advances on films for food packaging based on chitosan.

Statistical optimization of medium components and physicochemical parameters to simultaneously enhance bacterial growth and esterase production by Bacillus thuringiensis.

Bacillus thuringiensis is a genus extensively studied because of its high potential for biotechnological application, principally in biocontrol techniques. However, the optimization of esterase production by this strain has been scarcely studied. The aim of this work was to select and optimize the physicochemical and nutritional parameters that significantly influence the growth and esterase production of B. thuringiensis. To this purpose, 6 nutritional factors and 2 physicochemical parameters were evaluated using a Plackett-Burman design. Significant variables were optimized using a Box-Behnken design and through the desirability function to select the levels of the variables that simultaneously maximize microbial growth and esterase production. The optimum conditions resulting from simultaneous optimization of the responses under study were found to be 1 g/L glucose, 15 g/L peptone, and 3.25 g/L NaCl. Under these optimal conditions, it was possible to achieve a 2.5 log CFU/mL increase in bacterial growth and a 113-fold increase in esterase productivity, compared with minimal medium without agitation.