*Correspondent: Fax: + 60 4 6573678. e-mail: ccseow@usm.my Effects of frying parameters on physical changes of tapioca chips during deep-fat frying Chanderan K. Vasanti Nair, Chee C. Seow* & Guruprasad A. Sulebele Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 Penang, Malaysia Summary The interrelationships of the effects of frying time, oil temperature, and initial moisture content on moisture loss, oil absorption, and linear expansion of a tapioca starch chip half-product during deep-fat frying have been studied. Both oil absorption and linear expansion were affected, in different ways, by moisture loss. Oil absorption was essen- tially a quantitative water replacement process. On the other hand, linear expansion occurred as a result of rapid vaporization of water in the initial stages of frying, but reached a plateau before maximum moisture loss. Critical frying times, temperatures, and initial moisture contents, below which virtually no physical change occurred, were observed. The optimum set of frying parameters for maximum linear expansion appears to be a frying time of 40 s, an oil temperature of 200°C, and an initial moisture content of 15% (dry basis). Keywords Crackers, half-products, linear expansion, oil absorption, starch. Introduction Half-products have been defined as special food formulations that, upon immersion in hot frying oil, rapidly expand into a low-density, ready-to- eat, porous, and crisp product (Matz, 1984). These half-products, also known as intermediates, are normally produced by gelatinization of a starchy dough which is then shaped into different forms (usually thin chips) and dried to a horny consistency. One such product is keropok (or cracker) which is a popular snack food in Malaysia (Yu, 1993). Apart from the two essen- tial components (i.e. starch and water), other ingredients (such as fish or other types of seafood) are usually added to produce different types of crackers. Various aspects of keropok manufacture and formulation have been studied. Increased mecha- nization has led to greater productivity and prod- ucts of superior quality (Yu et al., 1981; Siaw et al., 1985). Studies on formulation have involved primarily investigations on the effects of different types and amount of starch on the linear expan- sion and crispness of fish keropok (Yu, 1991a,b, 1993). The amylose:amylopectin ratio of the starches used appears to be a major factor affecting the expansion and texture of the fried end-product (Mohamed et al., 1989; Haryadi, 1994). Insufficient water in the formulation causes incomplete gelatinization of the starch during steaming, resulting in a half-product that does not expand well on deep-fat frying. However, water in excess of the optimum level also limits expansion of keropok (Mohamed et al., 1989). Surprisingly, there is little information on how frying parameters (such as frying time, oil tem- perature, and the initial moisture content of the half-product) influence important physical changes (e.g. moisture loss, oil uptake, and vol- ume or linear expansion) that occur during deep- fat frying of low-moisture half-products. Such physical changes have a direct bearing on the physical attributes and acceptability of the expanded end-products. For example, crispness, International Journal of Food Science and Technology 1996, 31, 249–256 © 1996 Blackwell Science Ltd 249