Physicochemical Properties of Flaxseed Oil-Oligosaccharide Emulsion and Its Application in Food Products

Abstract

Growing awareness about the role of diet and quest for human wellness has fuelled interest in functional foods and functional attributes of many traditional foods that are being reinvented. Flaxseed continues to surge forward in its recognition as a functional food and has recently gained attention in the area of cardiovascular disease and anti-inflammation because it is the richest known source of α-linolenic acid (ALA). Because of the high content of this fatty acid, flaxseed oil is used as a food supplement, where enrichment with n-3 fatty acids (FA) is needed. The high content of ALA in flaxseed oil is, however, highly susceptible to oxidation, leading to rapid deterioration of quality. Study regarding incorporation of flaxseed oil as a source of ALA in functional food formulations has been little conducted. Therefore, this study was conducted to develop physically and oxidatively stable emulsion using flaxseed oil, and its application in food products enriched with n-3 FA. The objective of the first part of the study was to develop a practical and simple method to produce flaxseed oil emulsion with fructooligosaccharide (FOS). Effects of types and concentrations of emulsifiers and the ratio of dispersed phase to continuous phase in the emulsions on the physical properties (rheological property, particle size distribution, and emulsion stability) were tested. Among tested emulsifiers with HLB of 4.3, 8.6, 11.0, 14.5, and 15.0, the emulsion containing decaglycerol monolaurate (HLB 15) was the most stable. The concentrations of decaglycerol monolaurate above 2% (w/w) were able to form stable emulsions. Increase in emulsifier concentration increased viscosity and decreased particle size, showing pseudoplastic flow. All the tested ratios (3:7, 4:6, 5:5, 6:4, 7:3, and 8:2, weight basis) of the flaxseed oil and FOS except for 8:2 formed stable emulsions. The flaxseed oil emulsion using different ratios of flaxseed oil to FOS changed little flow behavior index. Oil in the emulsion was less oxidized than flaxseed oil itself, but was oxidized more than flaxseed oil added with TBHQ. These results suggest that the addition of FOS to the continuous phase of flaxseed oil emulsion may increase physical and oxidative stability of the emulsion. The objective of the second part was to determine the physicochemical properties and sensory characteristics of set and stirred yogurts added with flaxseed oil-fructooligosaccharide (FOS) emulsion. Descriptive analysis and preference test were carried out for six yogurts (set whole milk yogurt, set whole milk yogurt added with flaxseed oil-FOS emulsion, set non-fat milk yogurt added with flaxseed oil-FOS emulsion, stirred whole milk yogurt, stirred whole milk yogurt added with flaxseed oil-FOS emulsion, and stirred non-fat milk yogurt added with flaxseed oil-FOS emulsion). The addition of flaxseed oil-FOS emulsion little affected the physicochemical properties (pH, acidity, solid content, and color values) of the yogurts. The addition of flaxseed oil-FOS emulsion in the yogurts resulted in a large increase in ALA concentration. Fifteen trained descriptive panelists evaluated the six yogurts on a 16 cm structured scale. The descriptive analysis showed significant differences (p < 0.05) among the samples for 13 of 14 descriptive attributes. In descriptive analysis, the yogurts fortified with flaxseed oil-FOS emulsion were fishier than the yogurts without flaxseed oil-FOS emulsion regardless of the yogurt types (p<0.05), and the non-fat milk yogurts added with flaxseed oil-FOS emulsion were fishier than the whole milk yogurts added with flaxseed oil-FOS emulsion (p<0.05). Preference test indicated that the addition of the flaxseed oil-FOS emulsion did not have much impact on all attributes of the stirred whole milk yogurts (p>0.05). The last part of this study was conducted to assess the effects of flaxseed oil and dried whitebait as a source of n-3 FA, which could be used to produce eggs enriched with n-3 FA, and FOS as a source of prebiotics on performance of hens (commercial Hy-Line® Brown laying hens), and FA composition, internal quality, and sensory characteristics of the eggs. Dietary FOS increased egg weight. The amounts of ALA, eicosapentaenoic (EPA), and docosahexaenoic acids (DHA) in the eggs from the hens fed the flaxseed oil alone or flaxseed oil + dried whitebait diets were higher than those of the control. Hedonic scores for off-flavor, fishy flavor, buttery taste, and overall acceptability of the eggs from the hens fed the diet containing flaxseed oil + dried whitebait were lower (p<0.05) than those of the control. Overall acceptability of the eggs from the hens that had been fed the diet containing soybean oil + dried whitebait was lower (p<0.05) than that of the control. However, all the sensory attributes of the eggs from the hens that had been fed the diet containing flaxseed oil, dried whitebait, and FOS were not significantly different from those of the control. These results confirmed that flaxseed oil in the diet for laying hens increases the ALA content in the laid eggs and a combination of flaxseed oil and dried whitebait in the diet increases EPA and DHA in the eggs. Of significance was that the addition of FOS to the flaxseed oil + dried whitebait diet improved the sensory characteristics of the eggs enriched with n-3 FA compared with the flaxseed oil or dried whitebait diet alone.