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Item Partial hydrolyzed protein as an alternative stabilizer for peanut (Arachis hypogaea) butter(Elsevier Ltd, 2025-07-01) Thongkong S; Rakairyatham K; Tangjaidee P; Unban K; Klangpetch W; Phimolsiripol Y; Rachtanapun P; Rawdkuen S; Singh J; Kaur L; Issara U; Kingwascharapong P; Phongthai SPeanut protein hydrolysates with varying degrees of hydrolysis (DH) were prepared by using Alcalase and Flavourzyme. The enzymatic hydrolysis highly influenced a transformation of protein secondary structures, particularly from β-sheet to β-turn structures (11–21 %). The DH impacted functional properties and anti-free radicals' activity of peanut protein hydrolysates. Flavourzyme-derived protein hydrolysate (FPH) with DH5% had the maximum potential as an emulsifier (54.50 ± 0.71 %, p < 0.05). The effectiveness of protein hydrolysates in preventing the oil separation and enhancing the oxidative stability of peanut butter was dependent on the type of enzyme and DH. The inclusion of partial hydrolyzed protein (DH5%) produced by the Alcalase (APH) substantially decreased the occurrence of oil separation; whereas FPH with DH5% significantly retarded increment of PV, TBARs, CD in peanut butter during the storage period (p < 0.05). This study indicated the possible use of partial hydrolyzed proteins as a stabilizer in peanut butter by slowing lipid oxidation and increasing oil entrapment.Item Advanced platform for shelf life extension in liquid foods : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Bioprocess Engineering at Massey University, Palmerston North, New Zealand(Massey University, 2012) Brown, ColinThe shelf life of lipid based foods is often determined by the development of rancid flavours attributed to lipid oxidation reactions. These reactions are highly complicated and readily change when the reaction system is altered. As a result, researchers have struggled to make significant advances in their understanding of the mechanisms and rates of lipid oxidation. This thesis focuses on the generalised three step mechanism of lipid oxidation and develops understanding, through mathematical modelling exercises, about the factors that influence the rates of lipid oxidation. More specifically, this thesis focuses on bulk oils, bulk oils with added antioxidants, oil-in-water emulsions and the effects of oxygen supply and consumption rates in real food systems. For this thesis, methods were developed to identify and validate findings that suggest that lipid hydroperoxides are the rate defining reactant in lipid oxidation reactions. These methods were then used to measure the solubility of oxygen in oil and to define the role oxygen plays in determining the rates of lipid oxidation in a range of systems. The use of a newly developed batch oxidation apparatus led to the development and validation of models to predict the rates of oxygen consumption during oxidation. The model showed that the rates of oxygen consumption were half order with respect to the lipid hydroperoxide concentration. Through further validation experiments, it was shown that, during the initial stages of lipid oxidation before rancidity, each mole of lipid hydroperoxides formed required 5.04 moles of oxygen to be consumed when there was oxygen present. The same model and methods were then used to predict the changes in rates of lipid oxidation triggered by changes in reaction temperature. From this work, it was found that the Arrhenius law was capable of predicting the rates of oxygen consumption. The addition of butylated hydroxyanisole (BHA) to mixed fish oil samples brought with it a reduction in the rates of lipid oxidation, the magnitude of which was proportional to the concentration of BHA added. It was found that the inclusion of a modifier into the half order model was capable of predicting the rates of lipid oxidation when antioxidants were added. Methods to quantify the modifier were supplied for future use. The dilution of bulk oils by the formation of oil-in-water emulsions was also studied. It was found that the rates of lipid oxidation were proportional to the concentration of lipids in the emulsion. It was shown that the extent of oxidation during a batch oxidation was inversely proportional to the concentration of lipids in the emulsions as the aqueous phase acted as sump of oxygen for reaction in the oil droplets. Through modelling and short validation exercises, it was shown that changes to the surface area to volume ratio of oil droplets in emulsions had no effect on the rates of oxygen supply/lipid oxidation and that any effects noted in literature are likely to be the result of other surface active compounds. Finally, a modelling exercise showed that the rates of oxygen consumption via reaction were likely to be significantly faster than the rates of oxygen supply in unmixed systems in polymer packaging and, to some extent, open to the atmosphere. The diffusion of lipid hydroperoxides was shown to be important in bulk oils stored in polymer packaging as it allowed for a greater proportion of the oil to react with the oxygen transferred, thus reducing the potential for the oxygen supplied to take part in secondary and tertiary product formation. It was suggested that it is better, for a given quantity of oxygen supplied, for the entire oil product to react as it would result in fewer tertiary products being formed than if the oxygen were to be consumed at the surface of the oil only. Following this, it was suggested that an oil-in-water emulsion should be less stable than a bulk oil. Short experimental work showed that storing bulk oils in the absence of oxygen brings with it a decrease in the rates of lipid oxidation caused by a decrease in the concentration of lipid hydroperoxides. This decrease, coupled with anecdotal evidence that products do become rancid over long periods of time, suggests that the radicals formed during lipid hydroperoxide breakdown can be used in two different sets of reactions. That is, the relative rates of reformation of lipid hydroperoxide via reaction with lipids and the formation of tertiary oxidation products will likely determine the rates of lipid hydroperoxide breakdown and rancidity in real food systems. An indepth analysis of lipid hydroperoxide breakdown rates in the absence of oxygen as well as a set of validation experiments for the storage of bulk oils and oil-in-water emulsions in polymer films was suggested as being the final piece of information needed to complete a comprehensive model capable of quantitatively predicting the rates of lipid oxidation reactions and the shelf life of lipid oxidation prone foods.Item Studies on the antioxidant activity of milk proteins in model oil-in-water emulsions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology, Riddet Institute, Massey University, Palmerston North, New Zealand(Massey University, 2009) Ries, DanielThe present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.