Design, synthesis and characterization of fatty acid esters in food flavours and nutritional supplements

• Main Author: Li, Cheng
• Other Authors: School of Physical and Mathematical Sciences
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Science::Chemistry::Organic chemistry::Organic synthesis; DRNTU::Science::Chemistry::Analytical chemistry::Qualitative analysis; DRNTU::Science::Chemistry::Analytical chemistry::Quantitative analysis
• Online Access: https://hdl.handle.net/10356/55336
• Institution: Nanyang Technological University

Flavor esters are the most important and versatile components of flavoring compounds and fragrances. These esters have been widely used in the food, beverage, fine cosmetic, non-cosmetic and pharmaceutical industries. Methionol is an alcohol with low odour threshold ranging from about 1 to 3 ppm and imparts powerful sensory notes described as meaty, boiled potato-like, vegetable-like, savory or toasted cheese-like. 2-Phenethyl alcohol is a colorless liquid with a pleasant floral odour with a mild, warm and rose-honey-like note of moderate to poor tenacity. It has been wildly found in a variety of essential oils such as rose, hyacinth, aleppo pine, orangeblossom, ylangylang, allium, anise, carnation, geranium, neroli and champaca. This material is therefore used as a fragrance ingredient in many compounds, particularly when rose odour is desired. Novel methionol derived fatty acid esters of up to 14 carbon fatty acid and 2-phenethyl alcohol derived fatty acid esters of up to 18 carbon fatty acid were synthesized by both chemical and lipase catalysed esterification between fatty acids and methionol or 2-phenethyl alcohol, respectively. The high acid- and heat-stability of methionyl esters and 2-phenethyl esters meet the requirement of food matrix. Most importantly, the sensory test showed that fatty acid carbon chain length had important effects on the flavour attributes of methionyl esters and 2-phenethyl esters. Through Lipozyme TL IM-mediated tranesterification in solvent-free system, valuable methionol or 2-phenethyl alcohol derived esters were synthesized by using the readily available natural materials butter oil as the fatty acid source. The conversion of methionol or 2-phenethyl alcohol and yield of each methionyl ester or 2-phenethyl ester were also obtained by Gas Chromatography-Mass Spectrometry-Flame Ionization Detector (GC-MS-FID). The process parameters (reaction temperature, substrates molar ratio, enzyme loading, shaking speed and reaction time) were studied to achieve the highest conversion of 2-phenethyl alcohol to 2-phenethyl esters. Maximum conversion of 2-phenethyl alcohol (80.0 %) were achieved after 20 hours of reaction at 40 oC, shaking speed of 100 rpm, an enzyme loading of 20 % (w/w) of reaction mixture and molar ratio of 3.0:1 (mmol/mmol of 2-phenethyl alcohol to butter oil). This process was further optimized using response surface methodology (RSM) based on a three level- three-factor box-behnken design to investigate the effects of single and multiple interactive factors on the conversion. The optimum molar conversion (86.5 ± 2.6 %) were achieved for 2-phenethyl esters by using molar ratio of 4.0:1 (2-phenethyl alcohol/butter oil), 20 % enzyme loading of all the reactant at 137 rpm and 41 oC for 8 hours. Furthermore, the optimum condition may also provide a reference for the transesterification reaction for not only methionyl and 2-phenethyl esters but also other chemically derived esters. The transesterified butter oil may be directly applied as a flavouring ingredient or further processed to obtain pure aroma chemicals. This novel flavour ingredient can have applications not only in flavour and fragrance formulations (especially upon extraction and separation), but also directly in food products, such as cheese. The beneficial effects of both methods were compared qualitatively and quantitatively by GC-MS/GC-FID results. Compared by chemical method, the enzymatic ones seem a superior strategy due to the advantage of enzymatic reactions, such as high substrate specificity, high reaction specificity, purer products, reduction of waste product formation and the milder reaction conditions. Moreover, the transesterification of butter oil with methionol or 2-phenethyl alcohol reacted in solvent-free system have more advantage. This is because butter oil was applied as the inexpensive, readily available, and renewable natural precursors to synthesize flavor esters. Also, the solvent-free media was considered as safe in the food industry. Consequently, with the increase in consumer demand for natural flavoring materials, the use of specific enzymes in biosynthetic processes presents great potential to meet this demand. Nutritional supplements or nutraceuticals have aroused increasingly interest among the public. As one of such supplements, octacosanol has been the subject of numerous studies. Octacosanol is a water-insoluble and stable long chain fatty alcohol. In a long time study, it has been shown to have some health benefits such as cholesterol lowering, antiaggregatory effects, athletic performance improvment and cytoprotective effect.4-9 Thus, the high stability and encouragingly physiological function of octacosanol makes it a potential candidate for a supplement in food, beverage, pharmaceutical and cosmetics industries. In addition, the physicochemical and physiological properties of octacosanol are effective due to its high melting point; however, the poor solubility of octacosanol in oil becomes its largest obstacle for their application as nutritional supplements in food, beverage, pharmaceutical and cosmetic products. Consequently, in order to improve the solubility, new octacosanol derived esters were synthesized by both chemical-catalyzed and enzyme-catalyzed esterification of fatty acids with octacosanol. Besides, two synthesis methods were compared qualitatively and quantitatively. In our study, enzymatic method shows more advantages over chemical method, especially for the higher yield (>80 %) of enzymatic mehtod. Most importantly, the solubility of the esterified octacosanol were improved significantly which was up to 6 times that of octacosanol and our further study showed that different length of fatty acid carbon chain had effects on the solubility attributes of these esters. In addition, the hydrolysis test by lipase can prove that octacosanol derived esters can be digested by the human body. The increasing consumer demand for flavourful food and nutritional supplements supply has led to an increasing demand for food grade starting materials that may be considered natural. The use of specific enzymes in biosynthetic processes presents great potential to meet this demand. Due to the advantage of enzyme-catalyzed esterification or tranesterification, the esters in food could be synthesized through this strategy in the food industry.