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1 Spread out on tables (manually)

2 Optional; it is preferable to receive raw material without spines

3 Optional; this may be done after desalting, manually or mechanically

4 Optional; addition of spices

DESPINING2

Figure 13.1. Flow diagram for conditioning raw nopalitos for later processes. Adapted from Corrales-García (1998).

Cleaning and despining of nopalitos—the latter an obligatory postharvest practice for nopalitos—is usually done at the destination market just before the retail sale. This practice is generally carried out using a knife by people with highly developed skill. Nowadays, diced pads, whose spines have been removed, are packed in plastic bags and sold in Mexico and the southwestern United States.

Nopalitos whose spines have been cut off have higher metabolic activity and transpiration rates than do intact nopalitos. Also, mucilage leaking, wilting, and oxidation occur quickly, and their shelf life is short. For these reasons, despined and diced nopalitos are more perishable than is the intact product. In general, the main problems that limit shelf life of minimally processed nopalitos are brown discoloration at the cut surfaces (caused by polyphenol oxidases), mucilage leakage (undesirable mucilage accumulation inside the bag, which increases with dicing), unpleasant flavor caused by accumulation of anaerobic metabolites, and a surface yellowing, which leads to a color change from brilliant green to brownish green and gives them a cooked appearance. Vacuum packing of diced pads does not increase the shelf life at refrigerated storage temperatures (Rodríguez-Félix and Soto-Váldez 1992). Also, the type of packaging, the storage temperature, and the local atmosphere affect storage of minimally processed nopalitos. For instance, 4°C is better than io°C for storage up to 15 days, and polypropylene (25 pm thick) is better than polyethylene (35 pm thick).

Industrial Techniques

Many alternatives for processing cladodes, nopalitos, and tuna fruits have been described (Colin 1976; Corrales 1992b; Saenz 1995). Industrially processed nopalitos can last longer than fresh ones, allowing sales in distant markets. Also, the supply can be extended to other months, and prices and quality can be controlled. The variety of products obtained by industrialization adds value to the product and makes diversification of markets possible. Industrialization also generates rural employment, which contributes income that benefits the producer communities (Corrales 1992b). Today in Mexico some companies process nopalitos mainly for export, because domestic consumers prefer to buy fresh nopalitos and then cook them at home.

The first steps in industrial processing of nopalitos are reception and conditioning of the raw material, which should be of the highest quality and be despined by the grower (Fig. 13.1). Conditioning consists of scalding and washing. Scalding deactivates enzymes, destroys microorganisms, softens the tissues, and partially eliminates the mucilage. The main variables are temperature and duration of scalding, as well as additives that improve the product. Nopalitos of the wild nopal 'Tapon' (Opuntia robusta) lend themselves to higher temperature and longer cooking time than do cultivated nopalitos, such as the variety 'Milpa Alta' (Opuntia ficus-indica). The final product is washed with cold clean water, which fixes the characteristic green

Figure 13.2. Various brands and preparations of processed nopalitos available in Mexico as collected by the Programa Nopal (Cactus Pear Program) of Centro de Investigaciones Económicas, Sociales y Tecnológicas de la Agroindustria y la Agricultura Mundial (CIESTAAM), Universidad Autónoma Chapingo, México.

Figure 13.2. Various brands and preparations of processed nopalitos available in Mexico as collected by the Programa Nopal (Cactus Pear Program) of Centro de Investigaciones Económicas, Sociales y Tecnológicas de la Agroindustria y la Agricultura Mundial (CIESTAAM), Universidad Autónoma Chapingo, México.

color of nopalitos and eliminates adhering pectins and mucilage (Corrales-García 1998). The resulting nopalitos can be used for various products, e.g., nopalitos in brine, pickled nopalitos, and marmalades.

Nopalitos as Products In Brine

Nopalitos can be preserved in a saline solution (maximum 2% NaCl) and then canned, placed in plastic bags, or packed in glass or plastic jars to be used later to prepare various Mexican foods. More than 20 brands are currently available in Mexico (Fig. 13.2), many with their own preparation process. The conditioned nopalitos (Fig. 13.1) are commonly salted in large tanks containing 12% NaCl brine, using approximately 1.7 liters of brine for each kilogram of nopalitos (Fig 13.3). Nopalitos must remain in these tanks for at least 10 days and can be kept there for months. The high concentration of salt extracts water from the nopalitos, so salt must be added to maintain the brine. The tanks should be stirred daily with a wooden paddle.

Also, the tanks should be covered to avoid contamination and discoloration of the product by light.

When salting is finished, the product is taken to the process room, where it is desalted by washings (Fig. 13.3). Later, it is sorted, diced, and canned, or put into plastic bags or jars with a few spices and covered with 2% brine. The bags are sealed; the cans or jars are evacuated, covered, and sterilized in an autoclave or water-bath, then left to air dry before labeling. Bags, cans, or jars are packed in cardboard boxes and stored for the quarantine period; eventually they are shipped to the market. The product can also be sold in bulk without desalting (Fig. 13.3).

Compared with intact nopalitos (with spines), the final yield of nopalitos in brine ready for sale is about 57%, depending on the process and its control. The following procedures can improve success: (1) implement a well-defined program and rigorous quality control beginning with the reception of the raw material—e.g., remove pads that are bruised or flawed; (2) implement a quarantine program that maintains the product's quality for as long as possible; (3) avoid direct contact of the brine with a reactive metal (such

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