Properties of Fresh Meat: Shelf Life

  • Shelf Life vs. Retail Case Life

    • Shelf Life: the amount of time a meat product is acceptable for human consumption

      • begins at slaughter and extends through all phases of production, transportation, display, and consumer storage

        • determined by:

          • microbial contamination

          • microbial activity

          • proteolytic degradation (tenderness)

          • met-myoglobin reducing activity (oxidation)

      • If retail cuts are discolored at the “sell by” date or earlier:

        • marked down price

        • OR the package is discarded

          • ~2.55% of beef is discarded leading to a loss of $3.74 billion loss due to discoloration, annually (2022-2023)

    • Retail Case Life: refers to the duration that meat can be displayed in a retail setting before it must be sold or discarded, which can be shorter than the overall shelf life due to factors like temperature, humidity, and product handling.

      • consumers consider bright pink to bright red to be desirable lean color

      • deviation from this created a degree of unacceptability

      • quality is determined by consumers through appearance, so surface discoloration may be considered unwholesome

      • Retail meat packages are given a “sell by” or “pull by” date, which is indicative of the anticipated case life

        • 1 d = tenderloin, ground beef

        • 2 d = chuck, shoulder and round cuts

          • more surface area, changes color at a faster rate

          • locomotive cuts

        • 3 d = loin and rib cuts

          • change color as a slower rate, both lipid and color

      • New packaging technologies greatly extend the retail case life of meat beyond the times reported above

  • Deterioration of Quality During Retail Display

    • Muscle Pigment Oxidation

      • impacts flavor dramatically

      • Quality deterioration occurs because of lipid oxidation and muscle pigment oxidation

      • Muscle pigment oxidation negatively affects meat color

      • Some muscles discolor less rapidly than others because of:

        • increased (or conserved) metmyoglobin reducing activity (MRA), resulting from

        • Increased MRA and reducing equivalents allow the iron in myoglobin to remain in the reduced (Fe ++) state longer

        • (scavengers + mitochondria)

          • Scavengers will reduce the number of times it will go through the color change

            • antioxidant

    • Lipid and Muscle Oxidation

      • Lipid and muscle pigment are closely related; delaying one, slows down both

      • Lipid Oxidation

        • primarily affected by PUFA content of tissue

          • membrane-bound phospholipids

          • Poly Unsaturated Fatty Acids

            • the more it has the more likely it is going to go through lipid oxidation , which can lead to off-flavors, rancidity, and a shorter usable shelf life.

        • Unsaturated fatty acids undergo auto-oxidation by a free radical mechanism

          • abstraction of a labile hydrogen from the unsaturated lipid to form a lipid radical, followed by the addition of an oxygen molecule to form a lipid peroxyl radical

          • lipid peroxy radical undergo reactions, which form oxidation products

            • these oxidation products aversely affect meat color and texture

Lipid Oxidation

  • Lipid Oxidation

    • Five:

      • the breakdown of lipid hydroperoxides produces aldehydes, ketones and carboxylic acids

        • these compounds negatively affect meat odor and flavor

        • The retail case life (and ultimately the shelf life) of fresh meat

  • Antioxidants

    • Consumers prefer natural antioxidants

    • Antioxidants can extend shelf life of products

    • antioxidants are mainly classified into two types:

      • Synthetic antioxidants

        • common synthetic antioxidants are BHA, BHT, TBHQ, ascorbic acid and gallic acid esters

      • Natural antioxidants

        • includes antioxidants vitamins (Vitamin E and C) and phytochemical antioxidants

          • Phenolic compounds are the primary antioxidants present in herbs and spices

    • Mechanism of Antioxidant Action

      • antioxidants can be divided into three groups by their mechanism:

        • primary antioxidants which function as free radical terminators (scavengers)

          • useful in step 2 and step 3

        • Secondary antioxidants, which are important preventative antioxidants that function by stopping chain initiation

          • stops chain initiation

          • functions between step 1 and step 2

        • Tertiary antioxidants, which repair damaged biomolecules

      • Managing Oxidation

        • temperature

          • cold temperatures slow the oxidation reaction but cannot stop it — not even frozen temperatures

        • Anaerobic packaging

          • vacuum, modified atmosphere

        • Dark Storage

          • meat products are often stored and distributed in the absence of light to avoid photo-oxidation

          • Photo-oxidation: caused by the action of light

            • the oxidation of unsaturated fats is accelerated by expose to light

Feeding Vitamin E to Extend Shelf Life

  • Enhanced Meat Product Systems

    • Enhanced Meat

      • the addition of non-meat ingredients to whole muscle meat products to improve palatability, case life, and retail yield

      • also referred to as deep marination

      • solutions are injected into the meat product at low levels (~8-12% average)

      • Solution ingredients and their function:

        • water: yield juiciness and substrate

        • salt: flavor

        • alkaline phosphate: WHC

Older vaccine injection sites can cause green discoloration in meat; contained inorganic metals

  • would oxidize when exposed to the high levels of oxygen in the package

  • the injection site legions went away when producers were directed to use modern vaccines