Application of PEF technology and new smart ageing techniques to dry ageing venison and lean bull beef
Dry ageing of red meat is a re-emerging technique and product demand has increased considerably in recent years. Dry ageing of meat generates unique flavours and adds value. Most dry ageing is done on premium, highly marbled beef. With all its popularity, minimal research has been done on dry ageing of lean, low fat content animal models. In this research, the main focus was to study dry ageing in two lean red meat models, venison and bull beef with fast and slow oxidation, respectively. The two studies investigated the application of novel technology to enhance and add value to some low value cuts from lean bull beef.The first research project applied pulsed electric field (PEF), a standalone non-thermal technology, with the aim of improving meat quality attributes and enhanced moisture transfer in the dry ageing process. The results across the two trials showed that High PEF (HPEF-10 kV, 50 Hz, 20 µs) treatment had sufficient pulsed electrical field strength to cause cell electroporation; this was confirmed by the transmission electron microscopy (TEM) images that showed reduced myofibril organisation and deformation and rupture of z-lines. Application of HPEF improved drying rates during the dry ageing process by up to 6% in the two trials run at 65 and 80% relative humidity (RH). Ultrastructural modifications induced by HPEF treatment also caused improved meat tenderness by up to 9%. This is of considerable interest to meat processors as it would positively impact on consumer repurchase of the product. HPEF decreased the polyunsaturated fatty acids (PUFAs) throughout dry ageing but it did not affect cis 9, trans 11 conjugated linoleic acid (CLA) across both venison trials. The preference for CLA to be esterified on the sn-2 position of the triacylglycerol strongly reflects their oxidative stability regardless of the chosen ageing method of venison. The development of secondary oxidation by-products as assayed by thiobarbituric acid reactive substances (TBARS) was not influenced by PEF treatment. The PEF treatment groups had no effect on mineral content (including pro-oxidant transition elements) of meat samples. This was critically important as it showed that at the treatment level, little to no mineral leakage from the electrodes to the meat product was occurring. The derived changes in mineral content were due to the concentration effect between the dry ageing and wet ageing processes.The investigation into protein oxidative modifications showed similar trends to lipid oxidation with both PEF treatment groups not increasing total carbonyl content. Oxidative carbonylation increased in the dry ageing regime compared to the wet ageing process. To gather more information on specific protein oxidative modifications in the study, the protein oxidation biomarkers γ-glutamic semialdehyde (GGS) and α-aminoadipic semialdehyde (AAS) resulting from the oxidative deamination of proline, arginine and lysine residues, respectively, were investigated. No influence by PEF treatment was observed, but the AAS and GGS by-products were higher in dry aged venison compared to wet. The second part of this study was done in collaboration with AgResearch Ltd, and explored the use of novel smart ageing techniques by using stepwise in-bag dry ageing on lean bull beef. The study established lipid oxidation, protein oxidation and metabolite profile changes during ageing under standard operating conditions for in-bag dry ageing (stored at 2°C, 75% RH, with air velocity in chiller set at 0.5 m/s for 21 d). This was compared to treatment groups where air velocities were set at 0.5 m/s (T2), 1.5 m/s (T3) and 2.5 m/s (T4) all for 7 d and then the samples were vacuum packed for another 14 d. PUFA levels declined with exposure to the high air velocity treatment group (T4). These changes indicated that the increased chiller air velocity exposed the longer chain unsaturated fatty such as linoleic acid (C18:2tω-6 and C18:2cω-6) and linolenic acid (C18:3ω-3 and C18:3ω-6) were readily modified compared to lower air velocity (T2 = 0.5 m/s), although the changes were comparable with the control treatment group which was in-bag dry aged for 21 d. Other NMR-based lipid oxidation analyses on aliphatic to diallylmethylene proton ratios also confirmed these identified changes. Once again the CLAs showed high oxidative stability as they were not impacted by the treatment groups and the product across all treatments retained high antioxidant content in the form of α-tocopherols. The influence of the treatment groups and ageing time on the metabolomics of lean bull beef were investigated. The high velocity treatments did not affect metabolite profiles; however, the metabolite profiles were affected by ageing time (p < 0.05). As for protein oxidative modifications, treatments with high air velocity reported higher total carbonyl content. The oxidative biomarkers showed the same trend but their quantities indicate low accumulation levels.In conclusion, the represented studies reported in this thesis demonstrate the improvement in meat tenderness as a result of the PEF treatment application. The improved, regulated mass and solute transfer via PEF treatment and smart packaging technology has potential industrial application to increase product turnover and shorter processing time of this niche product. The stepwise ageing process offers the meat processor an opportunity to design the level of oxidative modification they would prefer as the air velocity has been shown to play a role in protein carbonylation.
Advisor: Bekhit, Alaa El-Din Ahmed; Carne, Alan; Birch, John Edward
Degree Name: Doctor of Philosophy
Degree Discipline: Food Science
Publisher: University of Otago
Keywords: ageing, “dry ageing”, “wet ageing”, “meat quality”, tenderness, “metabolite profiles”, PEF, “lipid oxidation”, CLA, “protein oxidation”, NMR, proteins, lipids, oxidation.
Research Type: Thesis