Amy Logan

Natural variation of bovine milk fat globule size within a herd

Native milk fat globule (MFG) size, pH, total fat, protein, and lactose composition in milk from individual cows was examined in autumn and spring 2012 and autumn 2013. Mean MFG diameters ranged between 2.5 and 5.7 µm. Some cows were observed to consistently produce small or large MFG throughout the sampling period, though trends were not consistent across all cows. Small-MFG milk contained more total polar lipids; however, the relative proportion of individual polar lipids did not differ with MFG size, with the exception of phosphatidylcholine, which was greater in small-MFG milk. No significant correlation between MFG size and proximate composition, including calculated fat yield or pH, was found. This work revealed a natural cow-to-cow variation in MFG size exists, which could potentially be exploited to improve the functionality of milk for manufacturing and some products.

Stabilization of Fish Oil‐in‐Water Emulsions with Oleosin Extracted from Canola Meal

International dietary guidelines advocate replacement of saturated and trans fat in food with unsaturated oils. Also, there is growing interest in incorporating highly unsaturated omega-3 oils in to food products due to beneficial health effects. A major obstacle to incorporating highly unsaturated oils in to food products is the extreme susceptibility to oxidative deterioration. Oil bodies were prepared from tuna oil, oleosin, and phospholipid mimicking natural oil bodies within oilseed. Oleosin was extracted from canola (Brassica napus) meal by solubilization in aqueous sodium hydroxide (pH 12) and subsequent precipitation at its isoelectric point of pH 6.5. The tuna oil artificial oil bodies (AOBs) readily dispersed in water to produce oil-in-water (o/w) emulsions, which did not coalesce on storage and were amenable to pasteurization using standard conditions. Accelerated oxidation studies showed that these AOB emulsions were substantially more resistant to lipid oxidation than o/w emulsions prepared from tuna oil using Tween40, sodium caseinate, and commercial canola protein isolate, respectively. There is potential to use commercial canola meal, which is cheap and abundant, as a natural source of oleosin for the preparation of physically and oxidatively stable food emulsions containing highly unsaturated oils.

Effect of Phytosterols on the Crystallization Behavior of Oil-in-Water Milk Fat Emulsions

Milk has been used commercially as a carrier for phytosterols, but there is limited knowledge on the effect of added plant sterols on the properties of the system. In this study, phytosterols dispersed in milk fat at a level of 0.3 or 0.6% were homogenized with an aqueous dispersion of whey protein isolate (WPI). The particle size, morphology, ζ-potential, and stability of the emulsions were investigated. Emulsion crystallization properties were examined through the use of differential scanning calorimetry (DSC) and Synchrotron X-ray scattering at both small and wide angles. Phytosterol enrichment influenced the particle size and physical appearance of the emulsion droplets, but did not affect the stability or charge of the dispersed particles. DSC data demonstrated that, at the higher level of phytosterol addition, crystallization of milk fat was delayed, whereas, at the lower level, phytosterol enrichment induced nucleation and emulsion crystallization. These differences were attributed to the formation of separate phytosterol crystals within the emulsions at the high phytosterol concentration, as characterized by Synchrotron X-ray measurements. X-ray scattering patterns demonstrated the ability of the phytosterol to integrate within the milk fat triacylglycerol matrix, with a concomitant increase in longitudinal packing and system disorder. Understanding the consequences of adding phytosterols, on the physical and crystalline behavior of emulsions may enable the functional food industry to design more physically and chemically stable products.

Seasonal variation of polar lipid content in bovine milk

Seasonal change of milk composition could offer opportunities for dairy manufacturers. A systematic survey on seasonal variation of six classes of polar lipids was conducted with 19 Holstein cows over the entire milking season using liquid chromatography-mass spectrometry technique. This study revealed that most polar lipid classes were positively correlated with the total fat content, but negatively correlated with fat globule size. All polar lipid classes displayed a large cow-to-cow variation as well as seasonal variation. All of the six classes showed a gradual increase over the milking season with the highest concentration observed in May (autumn). However, the proportion of different polar lipid classes remained constant during the entire milking season. This finding suggests that the production of polar lipids is highly regulated in the mammary gland. The implication of such a seasonal variation of polar lipids in the nutritional and technological aspects of milk is discussed.

Australian milk fat—Seasonal and regional variation of melting properties

The solid fat content and dropping point of milk fat obtained over 2 yr and from 19 bulk milk production sites across Australia were characterized. Solid fat content at 5 °C and 20 °C, respectively, ranged between 49.9 and 66.1% and between 14.6 and 29.6% across all sites. Dropping point ranged between 30.5 and 35.4 °C. The dropping point did not correlate with solid fat content at lower temperatures across several sites, indicating that it is not an accurate or useful measure of functionality at temperatures of 15 °C or below. Although at times, considerable variation was observed in milk fat melting properties between sites located in similar geographic regions, statistical analysis by means of boxplots and multidimensional scaling revealed broad similarities within regions over the 24 mo. Multidimensional scaling also revealed similarities between some quite distant and diverse regions (e.g., Queensland and South Australia with constant and seasonal production, respectively). These analyses were used to make 5 groups from the 19 sites to describe seasonal melting properties. The groups with sites in west Victoria, southeast Victoria, and Tasmania showed the largest seasonal variation and range of values, with peaks and lows in southeast Victoria and Tasmania occurring up to 3 mo later than in west Victoria. The group with sites in New South Wales, Queensland, and South Australia had the least variation and range of values, which were relatively high throughout. The group with Western Australian sites showed medium levels of variation but distinct seasonal patterns, with solids fats typically below and dropping points higher than the national average. The Victorian groups lows in dropping point occurred about 2 mo later than did the low values of solid fat content. No single factor stood out as determining the variation in melting properties.

Crystallization of Femtoliter Surface Droplet Arrays Revealed by Synchrotron Small-Angle X-ray Scattering

The crystallization of oil droplets is critical in the processing and storage of lipid-based food and pharmaceutical products. Arrays of femtoliter droplets on a surface offer a unique opportunity to study surfactant-free colloidlike systems. In this work, the crystal growth process in these confined droplets was followed by cooling a model lipid (trimyristin) from a liquid state utilizing synchrotron small-angle X-ray scattering (SAXS). The measurements by SAXS demonstrated a reduced crystallization rate and a greater degree of supercooling required to trigger lipid crystallization in droplets compared to those of bulk lipids. These results suggest that surface droplets crystallize in a stochastic manner. Interestingly, the crystallization rate is slower for larger femtoliter droplets, which may be explained by the onset of crystallization from the three-phase contact line. The larger surface nanodroplets exhibit a smaller ratio of droplet volume to the length of three-phase contact line and hence a slower crystallization rate.

Phytosterol crystallisation within bulk and dispersed triacylglycerol matrices as influenced by oil droplet size and low molecular weight surfactant addition

Phytosterols can lower LDL-cholesterol and are frequently used by the functional food industry. However, little is known regarding how phytosterol crystallisation can be controlled, despite solubilised phytosterols having improved bioaccessibility. This study investigates phytosterol crystallisation in bulk milk fat and in model dairy emulsion systems at two average droplet sizes, 1.0 and 0.2 µm. The effect of lecithin and monoacylglycerol addition on phytosterol crystallisation for both emulsion and bulk systems was also evaluated. Results demonstrated that lecithin and monoacylglycerols enrichment into the bulk system minimised phytosterol crystallisation. However, in emulsions, phytosterol crystallisation was mainly influenced by decreasing the droplet size. Smaller emulsion droplets containing lecithin showed the greatest potential for decreasing phytosterol crystallisation and had improved physicochemical stability. This information can be employed by the functional food industry to minimise phytosterol crystallisation and possibly improve bioaccessibility.

Trans Fats Replacement Solutions in Australia and New Zealand

Publisher Summary With increasing evidence to support that Trans Fatty Acids (TFAs) pose a higher risk of Coronary Heart Disease (CHD) compared to Saturated Fatty Acids (SFA), nutritional bodies continue to advocate reductions in TFA intake. Several countries have introduced legislation aimed at reducing dietary intake of TFAs. Denmark and several other European countries placed limits on the TFA content in foods that can be sold to consumers, while several other countries, including Canada and the United States, required that the TFA content is displayed on the product label if it exceeds a specified amount per serving. More recently, Singapore also has introduced TFA labeling regulations, while China is in the process of introducing legislation that makes it mandatory to declare TFAs on the nutrition label if partially hydrogenated fats have been used in product manufacture. Since the introduction of food labeling regulations, there have been marked declines in the TFA content in the food supplies of both Canada and the United States, and these reductions have been achieved without causing a significant increase in saturated fats. Australia and New Zealand are yet to introduce any compositional regulatory measures in relation to TFA in the food supply. Instead, the authorities have adopted a position of encouraging the food industry to voluntarily implement strategies to reduce the TFA content in the foods they manufacture. This chapter reviews various surveys conducted from 1970 onward on the TFA content of foods in Australia and New Zealand and discusses the measures adopted by regulatory authorities and industry to achieve a reduction in TFA intake by Australians and New Zealanders.

Strategies to Prevent Oxidative Deterioration in Oil-in-Water Emulsion Systems

Publisher Summary This chapter highlights that the ability to protect oil-in-water emulsion systems from oxidative deterioration has growing importance for the food and nutraceutical industries as new products are entering the market that have both enhanced levels of unsaturated Fatty Acids (FAs) and reduced levels of saturated and trans fats. Canola (Brassica napus) is the major oilseed crop grown within Australia and naturally contains high levels of antioxidants, including both α- and γ-tocopherols and phenolic acids. The predominant phenolic acid found in all Brassica oilseeds is sinapic acid and the major mechanism for the antioxidant activity of phenolic acids derives from their ability to scavenge free radicals by donating their phenolic hydrogen atoms. The resulting phenolic radical is resonance stabilized, with various functional groups either increasing or reducing this resonance stabilization. Tocopherols use a similar mechanism to protect against oxidative deterioration. Preheating canola seeds prior to oil extraction can further improve their inherent oxidative stability within bulk-oil applications. This is partly because the thermal decarboxylation of sinapic acid forms a potent lipophilic antioxidant, 2,6-dimethoxyvinylphenol, also known as 4-vinyl syringol (4-VS) or canolol. The chapter provides the details pertaining to this mechanism. Further, results from the study reported in the chapter show that fortification can improve the oxidative stability of 10% water-in-water tuna oil-in-water emulsions systems at levels of 5, 10, and 20% water-in-water total oil phase. Moreover, the results indicate that oil from preheated seed can provide protection from oxidative deterioration that is as good as or, in some cases, better than a selection of commonly used antioxidants.