Effect of co-extruded film on the shelf stability of sliced salted pork meat product

Thesis Abstract

The study evaluated the efficiency of co-extruded polypropylene (PP) and low density polyethylene(LDPE) in extending the shelf-stability of unam inung traditional meat product during storage underambient conditions. Fresh pork was processed, in traditional way, into unam inung meat product andstored for 6 months, under ambient room conditions as unpackaged, clay pot packaged (traditionalmethod), and those packaged in polypropylene (PP), low density polyethylene (LDPE) and co-extrudedpolypropylene/low density polyethylene (PP/LDPE). Samples were withdrawn at intervals of one monthfor evaluation of quality changes. Results show that the storage room temperature (25.95-27.91oC) andrelative humidity (68.25-77.42%) are suggestive of typical diurnal conditions during the beginning ofrainy season in South Eastern States of Nigeria. Relative humidity (RH) which was 69.55% at thebeginning of storage reduced to 68.29% in the 2nd month of storage and subsequently increased thereafterto 77.42% in the 5th month of storage. Due to increasing RH from the second month of storage, allproducts increased in moisture content, consequently leading to increases in water activity and reductionin crude protein, fat and salt content due to dilution effect resulting from mass action. These changes weregreater in the unpackaged and clay pot packaged samples due to greater access to air and moisture butleast in the PP/LDPE coextruded film due to greater restriction to air and moisture transmission. Owing toincreasing moisture and water activity from the second month of storage, protein hydrolysis became thedominant protein deteriorative reaction, leading to increases in protein solubility and pH, particularly inthe unpackaged but significantly least in the PP/LDPE co-extruded plastic film. Thiobarbituric acidreactive substances (TBARS) and free fatty acids (FFA) results suggest that both oxidative and hydrolyticrancidity were occurring in the samples but the extent was very low and did not lead to detectable

rancidity in any sample.

The reactions of the antioxidant vitamins (A,C and E) must have been effectivein preventing detectable rancidity, as they all have significant (p<0.05) correlations {r(VitaminC/TBARS) = -0.743, r(Vitamin C/FFA) = -0.586, r(Vitamin A/TBARS) = -0.882, r(Vitamin A/FFA) = -0.794, r(Vitamin E/TBARS) = -0.753 and r(Vitamin E/FFA) = -0.831}. All the vitamins continued toreduce during storage. Total viable count and mould count significantly (p<0.05) increased in theunpackaged samples throughout storage period presumably due to greater access to moisture and air.These counts reduced in the plastic film packages, particularly PP/LDPE package, probably due torestricted/lower availability of oxygen and moisture. Although all the sensory attributes slightly reducedduring storage, the reductions did not lead to significant loss of acceptability. All deteriorativereactions/changes were more adverse in the unpackaged samples and clay pot packaged samplescompared co-extruded PP/LDPE packaged samples. Thus, unam inung packaged with co-extrudedPP/LDPE plastic film is acceptable up to 6 months of storage at ambient room conditions without muchloss in quality. On the other hand, the unpackaged and clay pot packaged samples showed much

instability and spoilage that they were discarded after about 3 and 5 months respectively.