**1. Introduction**

In the sheep meat supply chain, quality traits such as colour, water holding capacity, texture, and oxidative stability are determined by various factors, including breed, finishing feed, and retail packaging method. High-oxygen modified atmosphere packaging (HioxMAP), using 70−80% O2 and 20−30% CO2, is a common meat retail packaging method due to its ability to maintain the "fresh" cherry red colour of meat. However, extensive research has shown an increased oxidation and lower eating quality of meat in HioxMAP compared with vacuum skin packaging (VSP) [1–3]. Trigas modified atmosphere packaging (TrigasMAP) is a more recently developed method in which oxygen is partially substituted with an inert gas, e.g., nitrogen, and has shown promising results in improving the eating quality and shelf life of meat [4].

The finishing feed of livestock is another factor affecting the quality of meat through altering the antioxidant activity in post-mortem muscles. The incorporation of antioxidants, such as vitamin E, or antioxidant-rich pasture crops were shown to result in reduced lipid oxidation and improved eating quality [5,6]. The use of oil crops and meals as animal feed supplements from the Brassica family, particularly camelina (Camelina sativa) has recently

**Citation:** Ha, M.; Warner, R.D.; King, C.; Wu, S.; Ponnampalam, E.N. Retail Packaging Affects Colour, Water Holding Capacity, Texture and Oxidation of Sheep Meat More than Breed and Finishing Feed. *Foods* **2022**, *11*, 144. https://doi.org/10.3390/ foods11020144

Academic Editor: Rubén Domínguez

Received: 14 December 2021 Accepted: 27 December 2021 Published: 6 January 2022

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gained attention in improving animal productivity and carcass value [7]. Camelina seed is known to contain essential fatty acids, such as alpha-linolenic acid and different phenolic compounds such as flavonoids and proanthocyanidins, which provides an opportunity to improve the oxidative stability of meat [8].

Animal breed or the genetic background is also known to influence the sheep meat quality. For example, pure Merino sheep is believed to produce meat that is less tender or darker in colour compared with meat from crossbred sheep. The differences in texture and colour are associated with carcass fatness, muscle glycogen concentration, muscle iron concentration, and/or post-mortem chill effects [9,10].

Many studies have demonstrated the effect of the three supply chain factors of breed, feed and packaging individually. However, little is known about their interactive effect or the extent to which each factor affects meat quality. Thus, the aim of this study was to investigate the quality of sheep topsides (*Semimembranosus*) and knuckles (*Vastus lateralis*) from Merino yearlings and Composite wether lambs, finished on three different diets (standard diet; standard diet supplemented with camelina forage; or standard diet supplemented with camelina meal), and packed in three retail packaging methods (VSP, HioxMAP or TrigasMAP). The CIELab colour, water holding capacity, texture, lipid oxidation and protein oxidation were measured.

#### **2. Materials and Methods**

#### *2.1. Animal Housing and Feeding*

Feeding experiments were conducted at the Agriculture Victoria Research, Hamilton Centre, Hamilton, VIC, Australia. All animal procedures were conducted in accordance with the Australian code for the care and use of animals for scientific purposes (National Health and Medical Research Council 2013). Animal ethics approval was granted by the Department of Jobs, Precincts and Regions (DJPR) Agricultural Research and Extension Animal Ethics Committee (AEC Code No: 2016-17). Details of the experimental design, feeding of animals, and slaughter procedures were described previously [7]. In brief, a subset of maternal Composite wether lambs (*n* = 21) and Merino wether yearlings (*n* = 21) kept in different pens selected based on their final liveweights were used for this study. The primal cuts were from animals randomly allocated to three finishing feeds: a standard pelleted diet containing grain and cereal hay (SPD), a pelleted mixture diet containing 15% camelina forage hay (SCF), or a pelleted mixture diet containing 8% camelina meal (SCM). Diets were formulated using the ingredients available in the major sheep producing regions. The metabolizable energy (ME) and crude protein concentrations of the diets were managed to be 10−11 MJ ME/kg dry matter and 14−15% crude protein.

#### *2.2. Slaughter Procedure and Collection of Sheep Primals*

The animals were transported approximately 250 km using a semi-trailer to a commercial abattoir and slaughtered after 18 h in lairage. At 5 days post-mortem, legs from the left side of the animals were collected. Topsides and knuckles from the legs were boned from the legs. The muscles were vacuum-packed using a Multivac C450 (Sepp Haggenmüller GmbH & Co., Wolferschwenden, Germany) with Cryovac® vacuum pouches (PA/PE 70, Sealed Air, Fawkner, VIC, Australia) with an oxygen permeability less than 65 cc/m2/24 h and water transmission less than 5 g/m2/24 h. The vacuum-packed muscles were frozen at −20 ◦C for 6 weeks.

#### *2.3. pH, Cutup, Packaging and Retail Display*

Following thawing at 2 ◦C for 24 h, meat cutup and packaging were conducted at approximately 6 ◦C. Prior to cutup, the pH of the muscle was measured using a spear-head pH probe attached to a WP-80 pH-mV-temperature meter (TPS Pty Ltd., Brisbane, QLD, Australia). *Semimembranosus* and *Vastus lateralis* were extracted from the topsides and knuckles. The muscles were cut into three sections from the anterior and randomly allocated to VSP, HioxMAP, or TrigasMAP packaging treatments. All packaging was conducted using a Multivac T200 (Sepp Haggenmüller GmbH & Co., Wolferschwenden, Germany). Meat samples were placed on a cello soaker pad (130 mm × 90 mm; CBS, Carrum Downs, Australia) inside a black Cryovac® MAP packaging tray (T0D0901C 170 mm × 223 mm, Sealed Air, VIC, Australia). The trays were sealed with a Biaxially Oriented PolyAmide/Polyethylene/Ethylene vinyl alcohol-based film (OTR 15 cc/m2/24 h). The gas composition in HioxMAP was 80% O2 and 20% CO2 while TrigasMAP had 50% O2, 30% N2, and 20% CO2. Vacuum skin packaging was conducted using Cryovac® Darfresh® film (OTR 4 cc/m2/24 h) and black Cryovac® trays (Sealed Air, Fawkner, VIC, Australia). Packaged samples were stored in a simulated retail display cabinet with LED lighting (~310 lux, Bromic Refrigeration, Ingleburn, NSW, Australia) at 4 ◦C for 10 days. The samples were rotated daily between shelves to minimise the effects of variations in illumination and temperature within the retail display cabinet on the samples.

#### *2.4. Instrumental Colour Measurement*

After 10 days in simulated retail display, CIE L\* (lightness), a\* (redness), and b\* (yellowness) were measured on the meat surface using a Minolta chroma meter CR-300 (Minolta Co., Ltd., Osaka City, Japan), calibrated with a white plate (no. 20733120; Y = 84.9; x = 0.3171; y = 0.3240). The colour of vacuum skin-packed samples was measured after a 30 min blooming at 6 ◦C, whereas the colour of HioxMAP and TrigasMAP samples were measured immediately after the samples were removed from packaging. Duplicate colour measurements were taken on each sample. Hue angle (h\*) and chroma (C\*) were calculated using the following equations:

$$\text{Hue angle} = \arctan\left(\mathbf{b}^\*/\mathbf{a}^\*\right)$$

$$\text{Chroma} = \sqrt{\left(\left(a^\*\right)^2 + \left(b^\*\right)^2\right)}$$

#### *2.5. Purge and Cooking Loss*

Purge loss was expressed as the weight loss in packaging during retail display. Samples were weighed before packaging (initial weight) and after 10 days storage (final weight). Excess moisture was removed with paper towel before weighing. Purge loss was calculated using the following equation:

Purge loss (%) = (weight before pack − weight after pack)/(weight before pack) × 100

Cooking loss was measured during the cooking procedure for Warner-Bratzler shear force and texture profile analysis. Each sample was weighed before cooking. After cooking, excess moisture on the meat surface was removed with paper towel before weighing. Cooking loss was calculated as:

Cooking loss (%) = (weight before cook − weight after cook)/(weight before cook) × 100
