Introduction
Shortening is a kind of edible fat which used traditionally in confectionery and bakery products. These fats are a homogeneous blend of various oils and fats, which are produced to provide desirable physicochemical and textural properties in flour and non-flour products. Shortenings prevent gluten and starch particles from adhering to each other and give the sensation of softness to the bakery products when chewed. Shortenings impart important functional properties such as tenderness and texture, aeration and stability, mouthfeel, heat transfer, positively contributing to the structure and geometry of the products and extended shelf-life. In bakery products, shortening increases the volume of the dough by allowing the gluten to regain its elasticity (1-3). Shortenings also help stabilize air cells produced during mixing (4).
Various types of shortenings, such as all-purpose, fluid, cake, icing, filler fat, bread, frying, pie crust, pastry, and dry shortenings are available in the food industry (1). Shortenings can be manufactured with or without emulsifiers (often mono- and diacylglycerols (2-4 % w/w)). Emulsified shortenings are more suitable for where the incorporation of air into the shortening system is desired (such as icings, cakes, etc.), while un-emulsified shortenings are typically used for cookies, crackers and frying (5). Final application of a shortening in the food industry typically depends on its solid fat content (SFC) profiles and oxidative stability. Such fats have to satisfy a host of nutritional, physical and rheological functionality requirements. According to the specific functionality requirements, the shortening ingredients are sometimes at odds with each other. For example, harmful trans fatty acids (TFA) are common ingredients required for good consistency and spreadability, whilst healthy essential fatty acids do not always aid in the consistency requirements (and should also be included in shortening formulation). The physical and rheological properties of shortenings depend on several factors including 1) type of fat base stocks and the amount of emulsifier; 2) the SFC profile; 3) the production process conditions (including temperature and mechanical agitation rate) (1).
Shortening production systems may, therefore, contain several steps such as blending, fractionation, hydrogenation, interesterification and tempering to obtain the desired crustal polymorph and melting characteristics. The hydrogenation is still the main technique for producing shortening in many parts of the world. Accordingly, this fat product may contain relatively high amounts of TFA (1). High levels of TFA in the diet can increase the risk of coronary heart diseases by increasing the level of triacylglycerol and the ratio of low-density lipoprotein (LDL) to high-density lipoprotein (HDL) cholesterol in blood plasma. It is specified that a 2 % increase in energy intake in TFA was led to 23 % increase in the risk of incidence of coronary heart disease. With increasing evidence of the harmful effects of TFA on human health such as an increased risk of cardiovascular disease and different types of allergies and cancer, studies, as well as regulatory policies, have focused on reducing the intake of TFA in diets (6, 7). In January 2006, the Food and Drug Administration of the United States of America (FDA) required producers to list the amount of TFAs on the nutrition facts label of conventional foods and some dietary supplements (8). Many countries such as USA, Brazil and EU countries have limits on the amount of industrialized TFAs in food products (9). In recent years, the Iranian National Standards Organization (INSO) has reduced the upper limit of TFA and saturated fatty acids (SFA) in food products. In this regard, the INSO revised the standard of specification of shortening in 2015, and changed the upper limit of TFA from 10 to 5 % and SFA from no limit to 65 % (10).
In recent years, many studies have been conducted to investigate the characteristics of shortenings worldwide. However, middle eastern products characteristics have not been well-studied, yet. The chemical composition and physical properties of 12 French shortenings; 73 brands of margarines and shortenings on the Danish market; and 10 Turkish shortenings have been characterized by Bayard and Wolff (11), Leth et al. (12) and Karabulut and Turan (13), respectively. Recently, Macias-Rodriguez and Marangoni (2016) investigated the rheological properties of nine commercial shortenings (including puff pastry, roll-in, all-purpose, cake and icing shortenings) with similar physicochemical characteristics but diverse functionality under small and large oscillatory shear tests (14).
In order to have accurate information on the intake of trans fats and to implement appropriate measures to reduce their intake, each country should have an updated estimate of the per capita consumption of TFA in the diet of its citizens. However, there is no report on the amount of TFA in shortenings in Iran. Other physicochemical and melting properties of this product are also not known.
In this study, the physicochemical characteristics (fatty acid composition, iodine value (IV), Lovibond color, free fatty acids (FFA), peroxide value (PV), oxidative stability index, slip melting point (SMP) and SFC) of commercial shortenings marketed in Iran were characterized. Hence, the present research can provide valuable information about different types of Iranian shortening.