C. González-Martínez

Use of vacuum impregnation in food salting process

Salting is an ancient preservation method, usually used separately or in combination with other processes such as air drying and pH lowering. Traditional salting processes are divided into brining and dry salting, each of them specifically applied for particular products. In this work, the use of brine vacuum impregnation (BVI) instead of dry salting or brine immersion (BI) at atmospheric pressure is discussed. The influence of different process variables (length of vacuum pressure period, temperature, sample structure and dimensions) is analysed, in terms of kinetic data and process yields, for meat (ham and tasajo), fish (salmon and cod) and cheese (Manchego type cheese). In general, BVI processes imply a notable reduction of salting time, increasing the process yields in line with the greater values of the ratio salt gain to water loss. Likewise, samples lose natural gas or liquid phases entrapped in their structure and reach a flatter salt concentration profile than that obtained in the conventional salting methods.

Microstructure and vacuum impregnation response of citrus peels

Abstract Vacuum impregnation (VI) technique represents a good choice for developing high quality peel products or food ingredients, taking advantage of their interesting composition, increasing their sweetness and improving their sensory acceptance. Vacuum impregnation response of citrus peels (orange, mandarin, lemon, grapefruit) were analysed using different isotonic solutions. Sample deformation and impregnation levels in line with pressure changes have been determined. Peel microstructure has also been analysed (by Cryo-SEM) before and after the VI process. Results reflect a high capacity of impregnation (45–70% of initial sample volume) and swelling (12–33% of initial sample volume) of the peels. The great porosity of the albedo zone is responsible for this behaviour. In this zone, the great intercellular spaces can be flooded by an external solution, and this makes the citrus peels highly suitable to obtain new products with improved functionality and sensory acceptance.

Changes in thermal properties of apple due to vacuum impregnation

Abstract Experimental determination and predictive equations are used to evaluate the effect of vacuum impregnation with sucrose solutions on thermal properties of apple samples ( Granny Smith ). Vacuum impregnation (VI) was carried out by immersion of samples in the sucrose solution and applying 50 mbar in the tank for 10 min; afterwards, atmospheric pressure was restored while samples remain immersed for 20 min. Thermal diffusivity was measured in non-impregnated (NVI) and impregnated samples in a transient heat conduction method. Thermal diffusivity changes due to VI were relatively low, whereas conductivity changes, calculated from thermal diffusivity, density and specific heat, showed very important changes. The proposed predictive model allows us to estimate changes in thermal properties due to VI in terms of product porosity and pore distribution and conditions of VI process.

Effect of Blanching and Vacuum Pulse Application on Osmotic Dehydration of Pear

Osmotic dehydration of pear cylinders (var. blanquilla) was studied by analysing the effect of blanching pre-treatment and the application of a vacuum pulse on the kinetics and yield of the process and on product quality (colour and mechanical behaviour). Fresh and stem-blanched samples were treated with 65 Brix sucrose at atmospheric pressure and by applying a vacuum pulse (50 mbar for 5 min). The influence of the sugar gain and water loss fluxes, and the tissue structural response to the vacuum pulse, on the total mass and volume losses of the samples has been discussed. Blanching implied an increase in the mass transfer rate in pear tissue. Vacuum pulse in blanched samples resulted in more volume compression than sample impregnation with the external solution due to the sample softening by thermal effect and to the partial gas release during its thermal expansion. This provoked the greatest volume losses and a reductionof the ratio of sugar gain to water loss, where the highest values reached were for non-blanched samples submitted to vacuum pulse. Mechanical changes induced by treatments were similar inall cases, but colour hue and chrome were better preserved in samples treated by PVOD. Nevertheless, this treatment implied a transparency gain due to the sample gas release and so, samples become darker.

Development of salt profiles on Manchego type cheese during brining. Influence of vacuum pressure

Abstract Cheese brining is a slow process, consistent with the low values of salt diffusivity through the liquid phase trapped in the protein matrix, especially at low temperatures. The action of hydrodynamic mechanisms (HDM) in the porous protein matrix might accelerate mass transport by introducing brine directly in the pores. Promotion of HDM occurs when pressure gradients are applied to the system (e.g. applying vacuum). The influence of pressure in the system on the developing salt concentration profiles during brining of Manchego type cheese was analysed. Salting was carried out at atmospheric pressure (BI), at vacuum pressure (50 mbar) (VI) and by applying a vacuum pulse at the beginning of the process which then continued at atmospheric conditions (PVI). In VI brining, the developed salt concentration profiles can be better modelled by an advancing disturbance front model than by diffusional equations. Curd porosity and moisture greatly affected salt transport kinetics, in this case.

Long Term Osmotic Dehydration Processes of Orange Peel at Atmospheric Pressure and by Applying a Vacuum Pulse

Osmotic dehydration is a useful tool to obtain orange peel products with good sensory acceptance and stability. Osmodehydration of orange peel has been carried out in different osmotic solutions (65 Brix sucrose, 55 Brix glucose and concentrated rectified grape must) at 40 and 50 C for different durations (0–10 days), at atmospheric pressure and by applying a vacuum pulse at the beginning of the process. Changes in sample composition (water and soluble solid contents), weight, volume, density and porosity were analyzed. In all conditions, samples reached the same sample solute content as the osmotic solution at about 24 h of treatment, and the concentration rate was faster when vacuum pulse was applied. Mass transfer behavior showed that impregnation of the peel pores occurred to a great extent, not only when applying vacuum pulse, but also in treatments at normal pressure, due to the capillary effects and pressure gradients generated in the tissue associated with structural changes. Impregnation contributed to compositional changes and weight development of the sample. The greater the osmotic solution viscosity, the lower the impregnation level at equilibrium, which was always promoted by vacuum pulse.

Optimisation of oat milk formulation to obtain fermented derivatives by using probiotic Lactobacillus reuteri microorganisms

Functional advantages of probiotics combined with interesting composition of oat were considered as an alternative to dairy products. In this study, fermentation of oat milk with Lactobacillus reuteri and Streptococcus thermophilus was analysed to develop a new probiotic product. Central composite design with response surface methodology was used to analyse the effect of different factors (glucose, fructose, inulin and starters) on the probiotic population in the product. Optimised formulation was characterised throughout storage time at 4 ℃ in terms of pH, acidity, β-glucan and oligosaccharides contents, colour and rheological behaviour. All formulations studied were adequate to produce fermented foods and minimum dose of each factor was considered as optimum. The selected formulation allowed starters survival above 107/cfu ml to be considered as a functional food and was maintained during the 28 days controlled. β-glucans remained in the final product with a positive effect on viscosity. Therefore, a new probiotic non-dairy milk was successfully developed in which high probiotic survivals were assured throughout the typical yoghurt-like shelf life.

Effect of the Osmotic Pre-Treatment on the Convective Air Drying Kinetics of Pear Var. Blanquilla

Kinetics of air drying of fresh and osmotically pretreated pear slices was analyzed. Osmotic treatments were applied for 0.5, 3, and 48 hours in 50°Brix sucrose solutions at 30°C. Air drying was carried out at 45, 55, and 65°C, 2.2 m/s air rate. Drying curves were modelled through a Fickian equation, obtaining the effective diffusion coefficient in each case. This coefficient was markedly affected by the temperature and by the osmotic pretreatment, ranging between 6.5 × 10− 12 to 5.8 × 10 − 10 m2/s. A significant relationship between the De, and the inverse of the initial solute content of the samples was found. Activation energy of the drying process was similar for fresh and osmotically pretreated samples for 0.5 and 3 hours, but increased considerably when long osmotic treatment time was applied. Total drying time increased in osmodehydrated samples, but process yield, in terms of sample weight loss, increased. These effects were more marked when long osmotic pretreatment times were used.

Edible chitosan coatings for fresh and minimally processed foods

Abstract: Chitosan is a biopolymer that shows great potential as an ingredient for the preparation of new edible films and coatings for different food applications. Chitosan has antimicrobial, antioxidant and emulsifying properties. Moreover, it is quite compatible with other biopolymers and lipids and thus can be used to formulate different film-forming dispersions adapted to specific target applications. This chapter reviews some of the most recent studies into the properties of chitosan-based film-forming dispersions, either containing chitosan alone or in combination with other food ingredients. The most relevant results of current research on the properties of chitosan-based composite coatings are also presented. Some examples of recent applications of chitosan-based coatings are reviewed and discussed as a foundation for the development of new chitosan-based coatings with improved functionality and performance.

Probabilistic models of food microbial safety and nutritional quality

Microbial and compositional analyses of processed foods, raw materials, ingredients and discharge streams are an important part of safety and quality assurance in the food industry. Law mandates that their results ought to be kept for a specified time. The records are usually in the form of charts or tabulated values presented or listed in a sequential order. Such records frequently appear as randomly fluctuating time series. Usually, the fluctuations are within a range considered safe or acceptable, and as long as the entries are all within this range the nature of the fluctuations is of little interest. Occasionally, there are exceptional entries; a high microbial count or a particularly low concentration of an important nutrient, for example. In most cases they can be traced to a known cause, equipment failure and human error are the most common. But there can be odd entries, which may have serious safety or quality implications that have no apparent reason. These occur because of the random coincidence of several factors, some unknown or undocumented. Usually they cancel one another, but not exactly, and hence the fluctuations. The probability that factors that tend to spoil the product, or lower its nutritive value, will act in unison can be estimated from the distribution of past events, provided that the entries are independent and their series stationary. The concept is demonstrated with industrial microbial and other records having symmetric and asymmetric distributions. It was tested by comparing the estimated frequencies of large or small values with those actually observed in fresh data.