Metodología de trabajo

6.1

Introduction

The objective of adding value to several products has been accomplished as the project set out to do. Those muscles within the beef forequarter which have the best potential for added value via further processing have been identified. Recommendations have also been made on the cooking regimes to use to optimise the functional properties of further processed products. Along with the functional property added value aspect an inexpensive and easy method has been developed (matrix method), which allows the nutritional characterisation of any export lamb product originating from the saddle region (shortloin and rack section). Further recommendations are made on how this matrix method can be further utilized for other lamb products originating from the hindquarter and forequarter, as well as how it could be adapted to other species.

6.2

Beef forequarter functionality

6.2.1

Tenderness

It can be concluded that for the beef forequarter muscles tested that there are distinct differences in tenderness. The Infraspinatus is the most tender of the muscles tested, followed by the Triceps Brachi Longhead and the Supraspinatus. These are the muscles that are identified as having the best potential for adding value in further processing applications were whole cuts of meat are used such as ready meals.

The other muscles tested Triceps Brachi Medialhead, Latissimus dorsi, Serratus Ventralis and Pectorialis Profundus were found not to have as good a tenderness profiles as the other muscles. Therefore their application in further processing applications such as ready meals would be very limited. This is compounded for the Latissimus dorsi and Triceps Brachi Medialhead as these muscles are quite small so would yield very little product per muscle (animal). Also the Pectorialis Profundus is a large flat muscle so the range of cuts able to be fabricated from it would be minimal.

6.2.2

Cook loss

There was no significant difference between the muscles tested, for cook loss. This was because the variation in cook loss for the muscles was the same order of magnitude as the range of cook losses over all the muscles. Another reason that no differences were observed may be due to the long cooking time, which meant cook losses had adequate time to diffuse out of the meat compared to some other studies which heat up to an internal temperature then stop cooking (variation in cooking times can occur). The cook loss for the muscles ranged from 29% to 34% but the amount of variation meant that no significant differences could be detected. This also emphasises the fact that cooking losses are more dependent on cooking temperature than muscle type.

6.2.3

Shrinkage

No significant difference in shrinkage could be detected between the different muscles. This was not unexpected due to the fact that there was a large amount of variation encountered with the shrinkage measurements. The shrinkage values ranged from 30% to 48% but the variation was at least 12% for each muscle (i.e. 31%+-12% or range of 19% to 43%).

6.3

Functionality as effected by cooking regime

6.3.1

Tenderness

The tenderness was markedly affected by the cooking regime employed. The main factor being the cooking temperature the meat is subjected too. The best tenderness is achieved when the meat is cooked at a temperature of 60°C to 65°C. This has been linked back to the fact that this is the temperature at which the collagen fraction of meat denatures. Due to the variation encountered the tenderness at temperatures above 65°C could not be said to be less tender, but meat cooked at temperatures above 65°C was firmer to touch. This would be due to increased cook loss and actomyosin denaturation. One problem with the current tenderness measurements is that they only take into account the force needed to cut through the meat, whereas tenderness as judged by consumers is more a combination of force needed to cut the meat and juiciness (i.e. a

pieces of meat needing the same force to cut through but different juiciness’ will probably be judged differently for tenderness).

6.3.2

Cooking losses

Cooking losses were found to be very temperature dependent as expected. This temperature dependency is related to the temperatures at which the three major protein fractions of meat denature at. The first stage of cooking losses occur at a temperature of around 50°C at which temperature the myosin fraction is known to denature which results in a significant reduction in the water holding capacity of the myosin. The second stage of cooking losses occurs at around 60°C were the collagen fraction of the meat proteins denature. As the collagen denatures is loses its ability to hold it own structure and collapses, causing significant shrinkage of the meat, which causes the expulsion of meat from the meat by compresses forces. The third stage of cook loss occurs at around 70°C and corresponds to the denaturation of actomyosin, which significantly reduces its ability to bind water.

The cook losses were found to not be very time dependent. The cook losses increase rapidly within the first five minutes of cooking as the meat is heated up to temperature and it takes a few minutes for the cook loss too diffuse out. After ten minutes cooking about 80% of the total cook loss occurs (for one hour cooking). As any protein denaturation that is going to occur at a given temperature occurs quite rapidly. Any slight increases in cooking losses after ten minutes are believed to be due to diffusion limiting processes slowing the release of any cook loss.

6.4

Optimal cooking

It has been shown that about 69% of the total cook loss (when cooked at 75°C or higher) is associated with the denaturation of myosin (and collagen shrinkage) and the other 31% due to actomyosin. As myosin denatures at the relatively low temperature of 50°C (relative to usual cooking temperature for meat), this cook loss associated with myosin and collagen denaturation is inevitable. However it is possible to minimise the further cooking loss caused by actomyosin denaturation. If the temperature of the meat

is kept significantly below 70°C the amount of actomyosin denatured will be minimal hence the cook loss can be reduced (i.e. cook at a temperature of 60°C to 65°C).

The tenderness of meat is optimal also at a temperature of around 60°C, which is high enough to cause collagen denaturation and also corresponds to the temperature at which cook loss from actomyosin denaturation is minimised. Therefore meat cooked at this temperatures will have optimal tenderness and yield.

For health and safety concerns a 7D bacterial death has to be achieved for cooked meat products. Cooking at 60°C requires cooking for 12 minutes, while cooking at 65°C requires cooking for 1.45 minutes. Bacterial death is also temperature dependent but it must be remembered that the functional properties change very significantly with temperature. A high cooking temperature will achieve the desired bacterial death in a short period of time, but will be at the detriment of the functional properties. Where possible a cooking temperature of 65°C should not be exceeded to prevent excessive detrimental effects to the functional properties of tenderness and cook yield.

6.5

Nutritional properties of export lamb

By breaking down the products produced from the lamb saddle into their constituent components, collecting product yield data and nutritional data enabled the nutritional easy characterisation of many export lamb products. By combining the yield data (how much of a constituent component is contained within a selected cut) and the nutritional properties of the constituent component the nutritional properties of the saddle cut in interest can be calculated.

It has been found that the major source of variation is the ratio of lean tissue to fat tissue. The different types of lean tissue within the saddle region (loin eye from shortloin and rack section and tenderloin) are very similar in terms of nutritional properties and carcass grade doesn’t make any significant difference. The main difference of concern between grades as regards nutritional properties is the fat tissue to lean tissue ratio, which is different for different carcass grades.

This method of breaking down selected cuts into their constituent components should also work for other portions of export lamb i.e. hindquarter and forequarter sections. Adequate nutritional information for lean and fat tissue from the hindquarter region is already available from the USDA food composition database. Yielding information would have to be collected for these sections to be characterised and to assess the effect of grade on these sections.

The method should also work for other species such as beef, venison and pork. Unfortunately no literature for New Zealand products of these species could be found. Some cuts from other species like beef also contain a significant amount of intermuscular fatty tissue (i.e. fat between muscle seams). This intramuscular fat would have to be yielded out to see how much it varies and consequentially how much it effects the nutritional characteristics of these cuts.

It would be worth investigating all the lamb grades for the products that are to be sold, as it may be found that even though there are differences for lean to fat ratios for grades, they might not be large enough to warrant separate labels. This means that it may be possible to use one label for each type of product, instead of different labels for each product from different grades. An example of this is for lamb racks, for PX grade racks the fat level was 33g/100g whereas for YX grade lamb it was 31g/100g. This difference is minimal, similar comparisons arise when comparing other nutrients for the two grades as can be seen in table 6.1.

Nutrient YX Rack Section

PX Rack Section

Mandatory Per 100g Per 100g

Protein (g) 15.00 14.55 Fat (g) 31.02 33.07 Carbohydrate (g) 0.00 0.00 Sugars (g) 0.00 0.00 Dietary Fibre (g) 0.00 0.00 Calcium (mg) 10.00 10.00 Iron (mg) 1.44 1.42

Sodium (mg) 97.75 99.09 Saturated Fat (g) 15.48 16.51 Cholesterol (mg) 84.44 84.77 Calories 339.17 355.86 Voluntary Zinc (mg) 1.71 1.66 Phosphorous (mg) 128.99 123.63 Niacin (mg) 4.95 4.80 Thiamine (mg) 0.11 0.10 Riboflavin (mg) 0.25 0.24 Vitamin B6 (mg) 0.10 0.09 Vitamin B12 (µg) 1.72 1.68

Table 6.1 Nutritional properties of YX and PX grade rack section.

Due to the differences in nutritional properties being minimal it may be better to use one label for both grades which complies for both (i.e. if a label assigned for a PX grade product was placed on a YX grade product compliance would still be met). This would reduce the number of different types of label that would need to be used/produced and would allow easier implementation into a processing plant. This would be because all products processed to the same specifications would use the same label and grade differences wouldn’t have to be worried about, which means less chance of erroneous labeling in a production/processing environment.

Chapter 7