Estudio de la influencia de las variables de clasificación sobre las condiciones laborales

The food package must protect and contain the prod- uct from the place and time of preparation and man- ufacture to the point of consumption. The packaging materials have additional task in MAP technology.

The factors that affect MAP–induced atmosphere within the package are respiration rate, mass of prod- uct in the package, the optimal gas concentration of the fruit in the pack, the free gas volume in the pack, etc. (Geeson et. al., 1985; Hong and Gross, 2001). The other factors are the packaging film factors, such as permeability of film used for packaging and the surface and mass ratio in the package.

The permeability of film for CO2and O2are mainly determined by the material and the thickness of the film, the area of the surface, and the gas concentration difference between the outside and inside of the pack- age. Since the respiring minimally processed (MPR) products utilize considerable oxygen, suitable plastic film for this type of MPR should have a relatively high oxygen permeability to avoid an oxygen-depleted atmosphere within the package. The gas transmis- sion rates for some polymeric film used for MAP are shown in Table 7.1.

Plastic films used for MAP of fresh fruits need to have relatively high permeability to O2and CO2. Most films have higher permeability to CO2than O2 because of the solubility of CO2in polymer. It is sug- gested that the permeability of film used for MAP of respiring products need to be five times higher for CO2 than that for O2 to result in adequate O2 in- takes and CO2 outputs on the surface. Because an O2concentration of less than 10–12% has an effect on respiration of fruits products, it can be proposed that the effective O2concentration should be below 5–6% to prolong the shelf life of the product. At 2–3% O2, there is a high risk of anoxia. The max- imum tolerable CO2concentrations for many fresh products are in the range of 2–5%.

Active packaging system uses O2 and CO2 ab- sorbers in the sealed pack. Some of the absorbers

7 Minimally Processed Fruits and Fruit Products and Their Safety 119 being used are calcium hydroxide, activated charcoal,

and sometimes magnesium oxide. Sometimes C2H4 absorbers like potassium permanganate are used to prevent the accelerating respiring effect of ethylene.

Minimal Pretreatment Processing

The minimal process operations should be valuable adjuncts to MAP for successful extension of the shelf life of fruit commodities. These operations include washing to remove the nondesirable materials from the surface (soil, insects, pesticides, etc.) and cool the produce, trimming to remove unsound tissue, sepa- rating inedible portions from desirable edible seg- ments, cutting edible tissue into suitable shapes and sizes, cooling and temperature conditioning, and ap- plying food additives for pH adjustment, microbial control, oxidative reaction control, and texture mod- ification.

The choice of washing method of fruits is depen- dent on the purpose of washing and the delicacy of the tissue. The wash water should have a low mi- crobial count and a suitable temperature for effective cleaning. Chlorine is the most widely used among the sanitizing agents in wash water available for fresh produce. However, the most that can be expected at permitted concentrations is a 1- to 2-log popu- lation reduction and the reaction of chlorine with organic residues can form potentially mutagenic or carcinogenic reaction products (Sapers, 2003).

Tissue shearing involves trimming, pitting, peel- ing, and coring. Such shearing actions cause de- compartmentalization of cellular components and the bruising of tissue near the shear surfaces. Both de- compartmentalization and bruising of tissue lead to oxidative reactions such as the enzymatic browning reaction with the consequence of product darkening and off-flavor development. The presence of cut sur- faces with a consequent release of nutrients, the ab- sence of treatments enables to ensure the microbial stability, the active metabolism of fruit tissue, and the confinement of final product enhance the growth ex- tent of the naturally occurring microbial population in minimally processed fruits. The low-acid fruits such as cut melon and tropical fruits can also favor the pro- liferation of pathogenic species such as Salmonella spp. and enteropathogenic Escherichia coli up to the infective threshold.

Another problem that necessitates further phys- iological and biochemical studies is that cut fruit products can lose rapidly their typical flavor and

develop loss of freshness even in refrigerated storage, due to changes in some volatile aroma compounds (Lamikanra and Richard, 2002).

Cooling and temperature conditioning are used to decrease the respiratory activities and control the propagation of microorganisms. Cooling methods for removing the thermal energy include forced-air cooling, hydro-air-cooling, hydro-cooling, ice con- tact cooling, and vacuum cooling, selected according to fruit characteristics.

Tropical and subtropical fruits and some temper- ate fruits are susceptible to a low-temperature tissue disorder called chilling injury. Generally, the lowest injury-safe temperatures for fruits and vegetables are in the range of 5–13◦C.

Spoilage control is one of the most important fac- tors of MAP fruits and fruit products. For fruits with pH values below 4.5 yeast, lactic acid bacteria, and fungi are the major contributors to spoilage. Chlorine in wash water is effective at a level of 10–200 ppm to inactivate molds, yeasts, and bacteria. For effective bacterial control, the chlorinated water must have a pH of 6 or lower. Sometimes hot water is used be- fore peeling to reduce the microbial load on the sur- face. The temperature used is between 45 and 62◦C, but some fruits such as berries are sensitive to hot water.

Food additives diffused or infused into fruit tissues are used in reducing the pH, modifying the textural at- tributes, inhibiting microbial growth and preventing discoloration. Some fruits may have pH values above pH 4.6 and under MAP conditions, spoilage and pos- sibly human pathogen growth may occur. Generally, as the pH of a cut produce decreases, there is less growth of spoilage and human pathogens. Lemon juice, citric acid, or ascorbic acid can be added to cut fruits for pH adjustment prior to MA packag- ing. Calcium in plant tissues is involved in the delay- ing of senescence, reducing respiration, decreasing ethylene production, increasing tissue firmness, and preventing enzymatic browning. The increase in tis- sue firmness with an elevation of tissue calcium is caused by the interaction of the calcium ions with pectin polysaccharides in both the middle lamellae and parenchyma cell walls. Control of browning is important to the feasibility of fruit processing. Un- til recently, the most commonly used agents to pre- vent enzymatic and nonenzymatic browning were sulfites which were multifunctional; besides inhibi- tion of browning they could control the growth of microorganisms, acted as antioxidants and carried

out other technical functions. However, they were corrosive, destructive to some nutrients, and could produce softening and off-flavors. The use of sulfit- ing agents to prevent the browning of fresh-cut fruits and vegetables was banned by the U.S. Food and Drug Administration in 1986. The review of Laurila et al. (1998) shows that the inhibition of brown- ing in minimally processed fruits and the search for practical and functional alternatives to sulfite agents have received a great deal of attention but with lim- ited success. Apple slices treated with combinations of some reducing agents, enzymatic inhibitors, and calcium-containing compounds derived from natu- ral products resulted in the extension of storage life and better maintenance of quality (Buta et al., 1999).

One of the important stages of pretreatment pro- cess is draining. After the peeling, slicing, and disin- fection washing, the high water content on the surface serves as a good environment for the propagation of microorganisms. Thus, it is necessary to reduce wa- ter on the surface. The most effective draining is cen- trifuging and removing about 2–3% water content from the surface, depending on the type and texture of the fruit.

The final stage of processing is packaging. The pretreated product is placed into the pack and sealed. Sometimes, vacuum is used to reduce the oxygen con- tent of the fruit tissue. A mixed gas with increased CO2and reduced O2is introduced into the pack to provide a good environment to reduce respiration and to prolong the shelf life. It usually takes place in the packaging room, the most critical zone in the processing chain. This room has to be appropriate for the temperature of the product and the hygienic requirement of the processing.

Handling and Distribution

The quality of modified atmosphere packaged and minimally processed fruits or fruits products in the distribution chain is affected by many factors. The quality maintenance is aided by the following proce- dures in the distribution chains (Faith, 1994):

r minimizing handling frequency

r providing continued control of temperature, RH, CA conditions during storage and transport r transferring product from truck to refrigerated

storage immediately

r rotating products on a first-in/first-out basis r stacking individual cases no more than five cases

high.

The most important factor is the temperature. High temperature or its fluctuation increases the human risk of the product and decreases the quality and shelf life.

Temperatures to be used during processing and dis- tribution and their relationship to the sensitivity of products are described in Table 7.2.

MICROBIOLOGICAL SAFETY OF