(Editor’s Note: This is an online-only article attributed to the August/September 2018 issue.)
Deep-fat frying is a common cooking method that uses fat or oil as the heat transfer medium in direct contact with the food at a temperature above the boiling point of water. Among all types of fried foods, fried fish and fried chicken products make up a substantial percentage of the items sold at fast-food restaurants. According to the U.S. Census data and Simmons National Consumer Survey, 93.8 million Americans consumed fried chicken in 2011. This figure was projected to increase to 101.04 million in 2020. From the consumers’ standpoint, fried food palatability is related to unique organoleptic and sensory characteristics, including flavor, texture, and appearance.
During the deep fat frying method, oil serves as a heating medium and absorbs into food, increasing the total fat content. For example, lipid content of French fries increases from 0.2 to 14 percent, lipid content may reach 40 percent in potato chips, and raw fish with 1.4 percent reaches 18 percent fat after frying. Fried foods have become a health concern and high consumption of fried foods has been associated with conditions including hypertension, low serum HDL cholesterol, obesity, and type 2 diabetes. Furthermore, the frying process generates various lipid oxidation products, some of which have been linked to premature aging and cancer. Therefore, there is much interest in reducing fat uptake during deep-fat frying.
On the other hand, reducing the fat content in fried foods is not that simple since it affects organoleptic properties such as taste and mouthfeel. In a November 1999 issue of LWT-Food Science and Technology, authors indicated that selection of an appropriate food coating before battering is one possible means of reducing fat-uptake. An edible coating is a thin layer of edible material formed as a coating on a food product. These coatings can act as barriers to moisture loss, which is important commercially, and reduces fat uptake during frying.
The effectiveness of a coating material is determined by its mechanical and barrier properties, which depend on its composition and microstructure, and by the characteristics of the food product to which it binds. Hydrophilic biopolymers can be used as water binders in a coating to reduce water loss from the coat. If water loss can be reduced, oil uptake would also be reduced. Most commercial biopolymer coatings that are claimed to act like this to reduce fat uptake are polysaccharide coatings.
Polysaccharide-based coatings are low-cost, biodegradable, and water-soluble; they do not require organic solvents before they are applied. Polysaccharides are hydrophilic, thus have poor water barrier property.
Starch. Starch is an abundant inexpensive biopolymer that can be obtained from corn, cassava, etc.
It consists of linear chain, amylose, and highly branched amylopectin. The predominant linear nature of amylose readily makes it easily form film. The amylose portion forms coherent, relatively strong, and free-standing films which are non-continuous and brittle. Starch films are odorless, tasteless, colorless, nontoxic, and do not interfere with the taste. However, the three hydroxyl groups per D-glycosylic unit impart a high degree of hydrophilicity to starch which does not favor its ability to lessons water escape.
Cellulose. Cellulose and its derivatives have been used as lipid barrier in deep-fat frying. Cellulose derivatives including hydroxypropyl methyl cellulose (HPMC), and hydroxypropyl cellulose (HPC), methyl cellulose (MC), carboxymethyl cellulose (CMC) have good film-forming characteristics. Cellulose and derivatives such as HPMC are able to form thermal gel to protect their content during frying.