Fried and dehydrated potato products

Abstract

Potatoes are the fourth most important vegetable crop in the world and the main utilization of processed potatoes includes table stock -31%-, frozen French fries -30%-, chips and shoestrings -12%-, and dehydrated items -12%- (Miranda & Aguilera, 2006). Potatoes are grown in approximately 80% of all countries and worldwide production stands in excess of 300 millions tons/year, a figure exceeded only by wheat, maize and rice. As the eating habits of consumers have become more sophisticated, much attention has been given to the quality of fried and dehydrated food, which is greatly affected by process- and/or storage-induced changes. Processed potato products such as potato chips have been popular salty snacks for 150 years and its retail sales in US are about $6 billion/year representing 33% of the total sales of this market (Garayo & Moreira, 2002; Clark, 2003).

Chemical composition of potato varies with cultivar, location of growth, agricultural practices, maturity at harvest, subsequent storage history, among others. Potatoes are mainly made up of water (75% on average). Starch, comprising 65–80% of the dry matter content of the potato tuber, is calorically the most important nutritional component. The composition of potato starch is about 21% amylose, 75% amylopectin, 0.1% protein and 0.08% phosphorus. The content of reducing sugars is closely related to the final color and acrylamide formation of the fried potatoes. For example, a maximum of 1 g/kg reducing sugars has been suggested as a way to diminish significantly the formation of acrylamide after frying. On the other hand, selecting of cultivars to fry that contain low levels of asparagine (another acrylamide precursor) may result in low-acrylamide fried potatoes (Friedman, 2003). Finally, the two main factors that influence sugar content of potatoes during post-harvest storage are variety and storage temperature. For frying, potatoes with high solids content (20–22%) are preferred, because they result in better texture, higher yields and lower oil absorption in the finished product (Lesinska & Leszczynski ,1989).

Deep-fat frying is one of the oldest and most common unit operations used for cooking foods by immersing them in an edible oil or fat heated above the boiling point of water (Farkas et al., 1996). This complex unit operation involves significant microstructural changes; in fact, most of the desirable characteristics of fried foods are derived from the formation of a composite structure: a dry, porous, crispy and oily outer layer or crust, and a moist cooked interior or core, whose microstructures form during the process (Bouchon et al., 2001). The high temperatures (around 160 and 180 °C) cause water evaporation, which is transferred from the food towards the surrounding oil, whereas oil is absorbed by the food replacing part of the released water. This process results in products with a unique flavor–texture combination (Mellema, 2003).

On the other hand, drying is one of the widely used methods of fruits and vegetables preservation. Water is removed to a final concentration, which assures microbial stability of the product and minimizes chemical and physical changes (Lewicki & Jakubczyk, 2004). Nowadays, drying is regarded not only as a preservation process, but also as a method for increasing added value of foods (Ramos et al., 2003). Processing of plant raw materials causes irreversible changes in the tissues of fruit and vegetables. These changes are particularly visible after heat treatment (Lisińska & Golubowska, 2005). In this chapter, it will be shown the most important issues related to unit operations used to process potatoes such as frying and dehydrating.