Thermal Food Processing

210 Thermal Food Processing: New Technologies and Quality Issues
defines commercially sterile as a “condition achieved by application of heat,
sufficient alone or in combination with other treatments and/or treatments to render
the product free of microorganisms capable of growing in the product at nonrefrigerated
conditions (over 10°C) at which the product is intended to be held
during distribution and storage.” Subpart X, Sections 381.300 to 381.311 of the
Code of Federal Regulations stipulate the thermal processing requirements for
canned poultry products. For a low-acid food receiving a thermal or other bacteriocidal
process, that process must be validated to achieve a probability of 10 –9 that
there are C. botulinum spores in the container capable of growing or a 12 log 10
reduction of C. botulinum, assuming an initial load of 1000 spores per container.
7.2.4 RENDERING
7.2.4.1 Current Research on Rendered Poultry
The demand for poultry meat has increased considerably in recent years. The
change in consumer preference for portioned or further processed poultry has
resulted in increasing amounts of by-products and underutilized products. Skin
and subcutaneous fat together account for about 19% of carcass weight. 56,57
The basic purpose of rendering is to produce stable products of commercial
value, free from disease-bearing organisms, from raw materials that are often
unsuitable or unfit for human consumption. Rendering involves two basic processes
of first separating the fat and then drying the residue. The most common
method used to extract fat from the tissue is heating. 58 Different types of thermal
processing are involved in rendering of poultry fat.
Piette et al. 59 inoculated one set of finely homogenized chicken skin samples
with Acinobacter sp., Bronchothrix thermosphacta, Candida tropicalis, Debaromyces
hansenii, Enterobacter agglomerans, Enterococcus faecalis, a Lactobacillus
spp. or Pseudomonas fluorescens, while the control samples were not inoculated.
Both samples were heated to 80 or 50°C to extract fat. Extraction of fat at
80°C resulted in nearly complete inactivation of the indigenous and inoculated
microflora, resulting in microbiological counts in the rendered fat of generally
below detection level. Conversely, large number of organisms (3.69 to 7.28 log 10
CFU/g) survived the 50°C extraction process.
A second study was undertaken by the same researchers 60 to determine the
influence of extraction temperature on the recovery of fat from chicken skin. A
maximum amount of fat (89.6% of the initial fat) was recovered from homogenized
skin heated to 80°, whereas the 50°C rendering temperature resulted in the
lowest fat recovery (51.5% of skin fat content).
Sheu and Chen 61 studied the yield and quality characteristics of edible broiler
skin fat obtained from five rendering methods: microwave rendering, conventional
oven rendering, water cooking, griddle rendering, and deep-fat frying. Microwave
rendering produced the highest fat yields (47.5%), followed by deep-fat frying
(33.4%), conventional oven baking (31.6%), griddle rendering (25.8%), and water
cooking (24.8%). The moisture content of the rendered skin fat was the highest