Meat Quality Slides PDF

Meat quality By: Arafa seifeldeen  Definition ▪ Meat quality is defined as the degree to which a specific product satisfies the needs and expectations of a particular buyer.  Groups of meat quality characteristics Quality Categories Individual Attributes Sensory quality...

Meat quality By: Arafa seifeldeen  Definition ▪ Meat quality is defined as the degree to which a specific product satisfies the needs and expectations of a particular buyer.  Groups of meat quality characteristics Quality Categories Individual Attributes Sensory quality Raw meat: visual texture, colour, visible fat, natural drip Heated meat: aroma, flavour, texture Technological WHC, PH value, protein, lipid and connective tissue properties, quality antioxidative status, emulsifying capacity, gel formation capacity Nutritonal quality Protein, moisture and lipid content, vitamins, minerals, digestibilty Product safety Microbiological quality, pesticides, heavy metals ions, antibiotics, hormones Ethical General welfare: handling, farming system, transport, slaughter considerations practices Farming system: feedlot, free range, organic farming and outdoor rearing Slaughter procedure: general handling and killing method  Continue introduction ▪ In general, meat is composed of moisture, protein, fat, minerals as well as a small proportion of carbohydrate, and the chemical composition of lean meat cuts is, on average, approximately ▪ 72% water ▪ 21% protein ▪ 5% fat ▪ 1% ash.  Continue introduction ▪ The most valuable component, from the nutritional and processing point of view, is protein. Moisture content is the most variable component of meat, and it is closely, and inversely, related to its fat content. ▪ The value of meat is essentially associated with its content of protein. methods for meat quality assessment  Moisture ▪ The largest part of meat consists of moisture, and it is important from both a sensory and technological point of view, as it influences eating quality factors, such as tenderness and juiciness, and the processing quality of the meat. ▪ As well as from an economical point of view as it contributes to the weight of the meat; moisture loss is weight loss.  Continue Moisture ▪ Moisture is the only component of meat that is substantially volatile at temperatures just above 100oC, the moisture content can be quantified by drying at such a temperature. Regarding the capacity for retaining the water in meat, in general beef has the greatest capacity, followed by pork, with poultry having the least.  Continue Moisture In general, moisture is evaluated by drying in an oven at 100-105°C until the sample reaches a constant weight. Alternatively it is also possible to use either freeze drying at room temperature for 96 h, or to use microwave (600 W) for 10 min.  Continue Moisture In any case it is important that the weighing is done precisely (0.1 mg) since weight is used for the calculation of the moisture content. The oven methodology the ISO (ISO 6496:1999) establishes that the difference between two repeated measures should be less than 0.1% (0.10 g for 100 g of samples).  Continue Moisture Meat before and after drying to obtain the moisture content.  Protein ▪ Typically, meat contains about 19% protein of which 11.5% is structural proteins – actin and myosin (myofibrillar), 5.5% is the soluble sarcoplasmic proteins found in the muscle juice, and 2% is the connective tissues – collagen and elastin, encasing the structural protein. ▪ Collagen differs from most other proteins in containing the amino acids, hydroxylysine and hydroxyproline and no cysteine or tryptophan.  Continue protein ▪ Elastin, also present in connective tissue, has less hydroxylysine and hydroxyproline. ▪ Hence the protein value in cuts of meat that are richer in connective tissue is lower. The content of connective tissue in these cuts makes them tough and often lowering their economic and eating quality values.  Continue protein Protein is the main component in meat that contains nitrogen, and the nitrogen content of meat is roughly constant. Therefore, the protein content of meat is determined on the basis of total nitrogen content, with the Kjeldahl method being almost universally applied to determine nitrogen content.  Continue protein ▪ Nitrogen content is then multiplied by a factor to give the protein content. This approach is based on two assumptions: 1. That dietary carbohydrates and fats do not contain nitrogen. 2. That nearly all of the nitrogen in the diet is present as amino acids in proteins  Continue protein ▪ On the basis of early determinations, the average nitrogen (N) content of proteins has been found to be about 16%, which led to use of the calculation N × 6.25 (1/0.16 = 6.25) to convert nitrogen content into protein content. The factor 6.25 is also used to convert total nitrogen in meat to the total protein content of meat.  Continue protein All references are based on Kjeldahl total nitrogen determination (ISO 5983-1:2005) based in the transformation of the organic nitrogen in ammonium ions by acidification followed by a distillation in basic environment and a final valuation.  Continue protein ▪ It is important to use a precise scale (0.1 mg) for the weightings. The percentage of total nitrogen is obtained using a factor of 0.14. From this percentage a factor of 6.25 is applied to convert the nitrogen to meat protein  Continue protein Digestion process to determine protein content.  Continue protein Distillation process to determine protein content.  Fat ▪ There are three main sites in the body where fat is found: 1. The largest amount of fat is in the storage deposits under the skin (subcutaneous fat) and around the organs (visceral fat or flare fat). This constitutes the obvious, visible fat in a piece of meat, and can be as much as 40-50% of the total weight in fatty meat or fatty bacon. This adipose tissue is composed largely of triglycerides. Clearly this visible fat can be trimmed off the meat during processing, before cooking or at the table.  Continue fat content 2. In smaller cuts and streaks of fat can be visible between the muscle fiber bundles, i.e. in the lean part of the meat; this is known as intermuscular fat and can constitute approx. 4-8% of the weight of lean meat..  Continue fat content 3. There are often small amounts of fat (flecks) within the muscle structure, belonging to the intramuscular fat or marbling or part of the structural fat, which includes phospholipids and to some extent long chain fatty acids. The amount of this fat fraction varies with the tissue, and can constitute of 1-3% of the net weight of muscle  Continue fat content There are basically two main methods to evaluate the fat content. 1. A method based on Soxhlet extraction (ISO 6492:1999) with or without previous acid hydrolysis and petroleum ether. 2. A method based on Folch method (Folch et al., 1957), extracting the fat with a mixture of chloroform and methanol.  Continue fat content Equipment used to determine fat content with Soxhlet method.  Ash ▪ Ash Meat contains a wide variety of minerals. ▪ The contents of iron, zinc and copper vary considerably in different species. ▪ High levels of minerals in the feed do not necessarily increase the level of mineral in the meat.  Continue Ash content ▪ Ash is the inorganic residue remaining after the water and organic matter (protein, fat, carbohydrates) have been removed by heating at high temperature (500-600oC) in the presence of oxidizing agents. This provides a measure of the total amount of minerals within a food.  Continue Ash content ▪ Analytical techniques for providing information about the total mineral content are based on the fact that the minerals can be distinguished from all the other components within a food in some measurable way. ▪ The most widely used methods are based on the fact that minerals are not destroyed by heating, and that they have a low volatility compared to other food components.  Continue Ash content ▪ The ash content of fresh foods rarely exceed 5%, although some processed foods can have ash contents as high as 12%, e.g. dried beef. Sodium chloride and phosphates are often the main component of the ash in many processed meat products.  Continue Ash content ▪ Usually ash is evaluated by means of muffle oven ‘ashing’ at 500-550°C. However, it is also possible to use microwave ‘ashing’. Since the measure is based in weighing, samples have to be weighed precisely (0.1 mg). ▪ The ISO (ISO 5984:2002) establishes that the difference between two repeated measures should be less than 0.10 g for 100 g of sample.  Continue Ash content Ash evaluation process, from left to right, fresh sample, weighing, muffle oven and ash  WHC The water-holding capacity (WHC) is the ability of meat to hold all or part of its water. one of the most important traits of meat quality. Weight loss due to purge or drip loss ranges from 2% to 10%. These losses produce an economic cost to meat processors and retailers.  Continue WHC In addition, drip loss is an important visual cue to assess meat quality. Several studies have suggested that consumers in most countries dislike drip loss in meat  Determination of WHC ▪ Each muscle was sliced to 2.0-cm in thickness, and processed into a disk with a diameter of 4 cm. Samples were put into netting and suspended in a plastic bag, ensuring that there was no contact between the sample and the bag. ▪ Samples were stored in this manner at 4°C for 24 h. The weight of each slice was recorded before and after being suspended.  Determination of WHC ▪ Drip loss was expressed as a percentage of weight loss after suspension relative to the initial weight of the slice. ▪ Drip loss was measured in 3 replicate samples from each carcass, with the average value recorded as the drip loss for each sample.  Summery of pork quality traits Traits n Average Median SD Minimum Maximu m IMF (%) 62 3.59 3.55 1.40 0.80 7.15 Moisture 62 73.80 73.88 1.02 70.60 75.95 (%) pH 60 5.93 5.93 0.14 5.71 6.29 Drip loss 62 2.89 2.41 1.55 1.00 7.62 (%) Cooking 62 23.00 23.48 2.70 16.85 28.90 loss (%)