Study On Preparation Of Functional Chocolate By Enzymatic Interesterification And Its Properties

Chocolate is one of the most popular sweet food for consumers, and cocoa butter is the main raw material for its production. Since the major composition of fatty acids in the cocoa butter is C16 and C18 saturated fatty acids, the traditional chocolate product has the disadvantages of high calories, harmful to the health and so on. With the improvement of living standards, consumer’s requirement for healthy chocolate product also increases. It is possible to prepare functional chocolate with potential health benefits and nutritional effects by modified cocoa butter with different fatty acids and triglycerides composition. Polyunsaturated fatty acids, such as linolenic acid, docosahexaenoic acid(DHA) and eicosapentaenoic acid(EPA), have important physiological effects, while they can not be synthesized by human body and must be obtained from food. Linolenic acid is mainly present in linseed oil, and EPA and DHA is the major component of fish oil. However, in daily life, people seldom eat these oils because they are easy to oxidize and have poor taste as well. Therefore, the intake of these unsaturated fatty acids can not meet the body’s nutrition needs. To solve the above problems, in this study, with the aim of not changing melting point significantly, the incorporation of polyunsaturated fatty acids into cocoa butter by enzymatic interesterification was explored. Subsequently, the fatty acids and triglycerides composition, solid fat content(SFC) and crystal shape of cocoa butters before and after interesterification were compared. After that, the modified cocoa butter was applied in the preparation of chocolate, and the sensory evaluation and shelf life of resulting chocolates were determined.(1) The simplest method for addition of polyunsaturated fatty acids into chocolate is to add oils containing polyunsaturated fatty acids into the chocolate formula. Therefore, according to the Chinese national standard of chocolate that the amount of other oil should be less than 5% of the total, a certain amount of cocoa butter and linseed oil were firstly mixed and the possibility of preparing chocolate which has the maximum amount of linolenic acid with the ratio of linoleic acid to linolenic acid being of(1~4):1 which is recommended by the WHO and FAO was investigated. The results showed that when the cocoa butter content in the chocolate formula was 38%(wt%), the ratio of linoleic acid to linolenic acid in the physical blending of cocoa butter and linseed oil decareased from 2.1:1 to 1:1 with the increase of linseed oil content from 1% to 3%. While the melting point of the blending decreased from 29.5℃ to 28.8℃, which was apparently lower than that of natural cocoa butter(32℃~35℃). Therefore, the physical blending is not able to prepare the required functional chocolate.(2) The interesterification of the blending of cocoa butter and linseed oil with the ratio of 38:3(wt%) was catalyzed by immobilized lipase Lipozyme TL IM. Aiming at obtaining the product with the melting point close to natural cocoa butter(NCB) and body temperature, the response surface method was adopted to investigate the effect of major factors, including reaction time, enzyme amount and reaction temperature, on the enzymatic interesterification. The optimum reaction conditions were determined as reaction time 110 min, enzyme amount 6%(w/w,%), temperature 58℃. Under which, the melting point of the resulting interesterified cocoa butter(ICB) is 36.5 ± 0.3℃.Compared with NCB, the content of linolenic acid in the ICB increased from 0.6% to 3.1% which was a 5.2-fold improvement, and the ratio of linoleic acid to linolenic acid reduced from 4.8:1 to 1.7:1. For the ICB, the major triglycerides were still POP, POS and SOS with the amount being of 62.6%, and the amounts of triunsaturated triglycerides(UUU) and diunsaturated-monosaturated triglycerides(SUU) with lower melting point increased from 0.9% and 6.8% to 10.5% and 13.6%, respectively. In the range of 5~37℃, although the SFC of ICB was a little lower than that of NCB, the variation trend of SFC with the change of temperature was consistent with that of BCB. The SFC of ICB is 1.6% at 37℃.The content of β forms in the ICB enhanced from 25.4% before interesterification to 26.8% after interesterification, suggesting that the ICB has greater stability. The acid value, iodine value and saponification value of ICB were 3.43 mg KOH/g, 41.7 g I2/100 g and 195.4 mg KOH/g, respectively, which meets the relevant national standards for cocoa butter. When the ICB content was set at 38% in the chocolate formula, the obtained functional chocolate has smooth surface and good taste with special flavor of cocoa butter and linseed oil. The shelf life of functional chocolate at 20℃ was 428 days, approximately 61 weeks, indicating that it has good storage performance.(3) In order to prepare the functional chocolate containing docosahexaenoic acid(DHA) and eicosapentaenoic acid(EPA), the interesterification of cocoa butter and fish oil with the ratio of 28:3(wt%) was catalyzed by immobilized lipase Lipozyme TL IM. Similarly, aiming at obtaining the product with the melting point close to NCB and body temperature, the response surface method was adopted to optimize the enzymatic interesterification and the optimum reaction conditions were reaction time 155 min, enzyme amount 7%(w/w,%), temperature 60 ℃. Under which, the melting point of the resulting ICB is 36.9 ± 0.3℃.Compared with NCB, the content of DHA and EPA in the ICB increased from 0 to 6.2%. For the ICB, the major triglycerides were still POP, POS and SOS(where P-palmiticacid, O-oleic acid, and S-stearic acid) with the amount being of 64.7%, and the amounts of lower melting point triglycerides of UUU and SUU increased from 0.9% and 6.8% to 6.6% and 17.8%, respectively. In the range of 5~37℃, although the SFC of ICB was a little lower than that of NCB, the variation trend of SFC with the change of temperature was consistent with that of NCB. The SFC of ICB is 1.7% at 37℃.The content of β forms in the ICB enhanced from 25.4% before interesterification to 26.9% after interesterification, suggesting that the ICB has greater stability. The acid value, iodine value and saponification value of ICB were 3.23 mg KOH/g, 42.0 g I2/100 g and 195.8 mg KOH/g, respectively, which meets the relevant national standards for cocoa butter. When the ICB content was set at 38% in the chocolate formula, The obtained functional chocolate has smooth surface and good taste with no fish odor but special flavor of cocoa butter. The shelf life of functional chocolate at 20 ℃ was 382 days, approximately 55 weeks, indicating that it has good storage performance.This study provides some theoretical and practical basis for developing functional chocolate containing polyunsaturated fatty acids, and it will have positive impact on promoting the development of chocolate industry in China.