Effect of Co-extruded Film on the Shelf Stability of Sliced Salted Pork Meat Product

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 under
ambient conditions. Fresh pork was processed, in traditional way, into unam inung meat product and
stored for 6 months, under ambient room conditions as unpackaged, clay pot packaged (traditional
method), and those packaged in polypropylene (PP), low density polyethylene (LDPE) and co-extruded
polypropylene/low density polyethylene (PP/LDPE). Samples were withdrawn at intervals of one month
for evaluation of quality changes. Results show that the storage room temperature (25.95-27.91oC) and
relative humidity (68.25-77.42%) are suggestive of typical diurnal conditions during the beginning of
rainy season in South Eastern States of Nigeria. Relative humidity (RH) which was 69.55% at the
beginning of storage reduced to 68.29% in the 2nd month of storage and subsequently increased thereafter
to 77.42% in the 5th month of storage. Due to increasing RH from the second month of storage, all
products increased in moisture content, consequently leading to increases in water activity and reduction
in crude protein, fat and salt content due to dilution effect resulting from mass action. These changes were
greater in the unpackaged and clay pot packaged samples due to greater access to air and moisture but
least in the PP/LDPE coextruded film due to greater restriction to air and moisture transmission. Owing to
increasing moisture and water activity from the second month of storage, protein hydrolysis became the
dominant protein deteriorative reaction, leading to increases in protein solubility and pH, particularly in
the unpackaged but significantly least in the PP/LDPE co-extruded plastic film. Thiobarbituric acid
reactive substances (TBARS) and free fatty acids (FFA) results suggest that both oxidative and hydrolytic
rancidity 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 effective
in preventing detectable rancidity, as they all have significant (p<0.05) correlations {r(Vitamin
C/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 to
reduce during storage. Total viable count and mould count significantly (p<0.05) increased in the
unpackaged 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 to
restricted/lower availability of oxygen and moisture. Although all the sensory attributes slightly reduced
during storage, the reductions did not lead to significant loss of acceptability. All deteriorative
reactions/changes were more adverse in the unpackaged samples and clay pot packaged samples
compared co-extruded PP/LDPE packaged samples. Thus, unam inung packaged with co-extruded
PP/LDPE plastic film is acceptable up to 6 months of storage at ambient room conditions without much
loss 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.