Chemical Properties
Table 1 presents the fatty acids composition of shortening samples. The TFA content of the shortenings varied between 0.21 and 15.54 % (4.29 % on average). Based on definition, fat products with less than 5 % and 2 % TFA are referred to as low-trans and trans -free products, respectively (16). According to Table 1, only 13.33 % of the samples (codes 5 and 11) were trans -free (containing less than 2 % TFA). Also, 66.67 % of the samples (codes 1, 2, 3, 6, 8, 9, 10, 13, 14 and 15) were low-trans (containing 2-5 % TFA), and 20.00 % of the samples (codes 4, 7 and 12) contained more than 5 % TFA. The major trans isomer of the shortening samples was elaidic acid (Trans 18:1) with a mean content of 3.52 %.
Although applying more stringent regulations of maximum allowed amount of TFA was partly successful, about 20 % of the shortenings found in the Iranian market still contained TFA contents of above 5 %, which could be the cause for concern. Unfortunately, there is no precise and reliable information on TFA content found in Iranian shortenings in previous years, but undoubtedly these series of changes in regulatory policy reduces the TFA content in Iranian shortenings.
As can be seen in Table 1, the SFA content of the shortenings was between 40.08 and 59.54 % (50.46 % on average). Palmitic acid was the main saturated fatty acid in the samples (25.48-48.90 %, 35.46 % on average). This finding indicates that the palm oil and/or its derivatives (palm olein and stearin) are the main fat base stocks for production of Iranian shortenings. Oleic and linoleic acids were the dominant unsaturated fatty acids (with a range of 26.96-38.78 % and 6.49-21.73 %, respectively). There was also a small amount of linolenic acid in Iranian shortenings (with a range of 0.11–1.83 %, 0.66 % on average), which helped their high oxidative stability.
The regulatory policy on the amount of lauric acid has recently focused on reducing the maximum level of this fatty acid in fat products due to increasing health concerns. In this regard, the INSO has determined an upper limit of 0.7 % for lauric acid in the last standard amendment of shortening (10). According to Table 1, the main content of lauric acid in Iranian shortenings was 0.26 %. However, the lauric acid content of sample 1 and 2 was respectively 1.08 and 1.32 % which was more than the standard limit.
Leth et al. (12) characterized the properties of all shortening brands in the Danish market (39 brands) from 1995 to 1999. They observed a gradual decrease in trans isomers in the Danish shortenings: the content of TFA in this product was reduced from 10.4% in 1992 to 3.6% in 1995 and Danish shortenings were almost free from transisomers in 1999. The SFA content of Danish shortenings was 29.9-42.8 %. They also reported that palmitic acid was the dominant SFA of Danish shortenings with a range of 24.1-28.0 %.
Karabulut and Turan (13) analyzed 10 shortenings in the Turkish market from 2003 to 2004. According to their results, the TFA content of the shortenings in Turkey was 2.0-16.5 % and SFA content was 36.3-43.1 %. Also, palmitic acid with the range of 23.8-38.4 % was the predominant SFA content in Turkish shortenings, approximately similar to the Iranian case.
In general, by decreasing the maximum limit of TFA in fat products, manufacturers have to increase the SFA content in fat formulations because TFA play a significant role in consistency, plasticity, and proper melting properties. Therefore, in order to compensate for this flaw, the increase in SFA is inevitable in fat formulations (12).
The IV is one of the important parameters of oils and fats, indicating their unsaturation level. There is a direct relationship between the IV and nutrition value of fat products. The INSO specifies no limit for the IV of shortenings. According to Table 1, the IV of Iranian shortenings was between 40.84 and 73.32 (53.52 on average).
Kheiri (17) reported the IV of 10 shortenings in the markets of Australia, Egypt, Netherlands, Japan, Kuwait, Malaysia, New Zealand, Turkey, United Arab Emirates, and United States of America as 57.0, 71.8, 67.0, 60.7, 60.4, 49.1, 48.3, 95.5, 75.9, and 84.4, respectively. Generally, it can be concluded that the IV of most Iranian shortenings is less than that of the foreign samples. Therefore, Iranian shortenings may be more saturated than the foreign ones (Table 1).
FFA content is among the most important quality parameters of oils and fats at all the processing and storage stages. These compounds are indicators for studying hydrolytic rancidity and are the secondary products of oxidation. By increasing the FFA content in fat products, the smoking point is reduced (18). According to INSO, the maximum FFA limit (wt. % of palmitic acid) is 0.1 %. As can be seen in Table 2, the FFA content of the shortenings was 0.02-0.92 %. In fact, 46.7 % of the samples’ (samples 5, 6, 7, 8, 9, 11, and 12) FFA contents was above the standard limit.
PV is an indicator of the initial oxidation products (hydrogen peroxides). Although hydrogen peroxide has no odor, the secondary products of oxidation such as aldehydes and ketones with the undesirable odor (off-flavors) are produced due to the breakdown of these compounds. The PV measurement is the most common quality test for oils and fats (18).
The PV of Iranian shortenings can be seen in Table 2. The PV of the Iranian shortening samples was 1.0-3.0 mEq/kg. According to the INSO, the maximum limit of PV of shortenings should be 1, 2, and 5 mEq/kg at the time of production, for import (at the time of importing goods), and at the time of consumption, respectively. As shown in Table 2, all the shortenings had the PV of less than 5 mEq/kg. In general, the samples with higher TFA and SFA contents had a lower PV; since the increase in the content of these fatty acids increases the oxidative stability of fat products.
Oxidative stability of oils and fats is affected by the presence of unsaturated fatty acids, oxygen content and storage conditions. The high content of unsaturated fatty acids accelerates the decay, thereby causing off-flavors, toxic compounds, loss of nutritional value, and unusable fat products. The toxic compounds resulting from rancidity can cause problems such as tumors, heart failure, cataract, and brain dysfunction (18). The high oxidative stability is one of the most important features of shortenings, which has a great impact on the shelf-life duration of final products (1). According to INSO (10), the IP110 of shortenings used in flour and confectionery products should be at least 30 and 25 h. According to Table 2, IP110 of the shortenings found in the Iranian market was 10.03-44.02 h. In fact, 53.3 % of shortenings (samples 1, 2, 3, 5, 7, 8, 11, and 13) had the IP110 below 25 h and was not in the standard range. However, 46.7 % of the samples (samples 4, 6, 9, 10, 12, 14, and 15) had IP110 above 30 h, indicating the high oxidative stability of these samples. Unfortunately, no information can be found on the oxidative stability of shortenings in other countries.