Sterilization is a critical step in the manufacture of wet
petfood. Its aim is to guarantee the microbiological safety of
products during their shelf life. Sterilization also has a
great influence on flavor development (mainly through Maillard
reactions) or off-flavor generation. Thus, sterilization is
considered a key factor for wet petfood palatability.
This article will focus on a study that evaluated the
influence of process parameters (time, temperature,
sterilization value (F0)) on the expression of a specific
palatability enhancer (PE1) in a chunks-in-jelly cat food
product, in terms of palatability. Consumption of Maillard
precursors was measured as well. Correlation between
palatability, process and chemical data was also carried
out.
The palatability enhancer (PE1) used was a complex mix of
Maillard precursors (amino acids and reducing sugars) together
with other ingredients. The study used a wet petfood product
containing 50% chunks and 50% jelly. The palatability enhancer
was added to the jelly (2%; i.e., 1% of the total weight). The
products were packaged in 100-g pouches.
Typical retorting processes of wet cat food range between
120°C and 130°C for 10 to 120 minutes, depending on product
type, packaging type and size. As a starting point (process 0),
performance of the palatability enhancer (PE1) added at 1% was
measured versus no palatability enhancer retorted at 127°C for
17 minutes (see Figure 1). Consumption of product was higher
(p<0.001) with the presence of PE1, demonstrating that
proper palatability enhancers are a key factor for palatability
of wet petfood.
Moreover, it was important in this study to find out how to
improve the performance of the palatability enhancer by using
different process conditions. Thus, an experimental design was
created to evaluate the effects of processing. Sterilization
values F0 were recorded for each process within the core of the
pouches. They were similar to theoretical F0 (data not shown). It is interesting to note
that products 2, 3 and 4 underwent similar F0 with different
process conditions.
Levels of the remaining reducing sugars and free amino acids
were also evaluated in the finished products. In particular,
the concentrations of two amino acids (AA1 and AA2) and one
reducing sugar (Sugar 1) were determined after the process.
Palatability tests (two-bowl tests) were performed with 40
cats. Each process was tested versus all four other profiles,
following a complete block design. The following parameters
were recorded (the first two are representative of palatability
of the products):
Level of significance for food consumption (student
test);
Process parameters do have an influence on the palatability of the chunks-in-gravy.The most palatable products were the products in which Sugar 1 and AA2 were the most consumed during the process.Average consumption of each product; and
Level of significance for the first food chosen (Khi-two
test; this parameter is related to the attractiveness of the
products).
The average consumption per cat (AC) was calculated for each
product. Means were compared through an analysis of variance
(ANOVA). For each test, a mark between -3 and +3 was attributed
to each product as a function of the level of significance for
food consumption. For example, in a test of A versus B, if the
consumption result was a significant difference (p<0.001)
for product A, A received a +3 and B was -3. If the result was
no significant difference, both products received a 0. The sum
of marks for level of significance for food consumption was
calculated for each product (the score significance). Scores
were compared through ANOVA. The same system was applied to
level of significance for the first food chosen (score first
choice).
These calculations revealed a statistical difference
(p<0.05) between average consumptions (AC) of products. Two groups can be distinguished here. Products 3, 4
and 5 (retorted for the longest time) were the most palatable,
whereas 1 and 2 were the least consumed. The same results were
obtained with score significance (data not shown). It is
interesting to note that products 2, 3 and 4 showed significant
differences in terms of palatability, although they underwent
the same F0.
Similar results were obtained for score first choice. Two groups can also be distinguished here: Product 2
(lowest score) and products 4 and 5 (highest scores). Products
1 and 3 show intermediate scores between the two groups. These
scores are not significantly different from either groups
(p>0.05). These results show that process parameters do have
an influence on the palatability of the chunks-in-gravy.
A principal components analysis (PCA) was carried out next.
This analysis allows products and variables to be represented
in a multi-dimensional space. PCA allows us to establish
similarities between products, as well as possible links
between variables. Only palatability variables were active. All other
variables were illustrative.
Results
Sterilization time has a significant effect on palatability
and on Sugar 1 and AA2 concentrations. This shows that the most
palatable products were the products in which Sugar 1 and AA2
were the most consumed during the process. As amino acids and
reducing sugars are precursors of the Maillard reaction, they
are consumed during the process and contribute to develop
flavors, making the food more palatable and attractive.
However, none of the process parameters has an influence on
AA1, showing that this amino acid does not significantly
undergo Maillard reactions.
Sterilization temperature (in the selected range) does not
show any significant effect (p>0.05) on palatability or
analytical data. Sterilization value F0 shows a significant
effect (p<0.05) on score significance, but not on
palatability or analytical data. P values show
that the effects of F0 on average consumption and score first
choice (non-significant at p<0.05), must be considered
(0.17p0.19). As F0 can be considered as a combination of time
and temperature, it seems logical to obtain P values that are
intermediate between that of time and temperature.
Products 4 and 5 (60-minute
process) are the most attractive and the most palatable
products, followed by products 3, 2 and 1. Based on these
results, there is an evident link between process, formulation
of palatability enhancers and palatability.
The use of a palatability enhancer is a key factor for
palatability of wet petfood, but utilizing the best
sterilization conditions an additional way to enhance
palatability. In this specific case study, the best solution
was to increase process time. Overall, this study proved that
palatability of chunks-in-gravy containing 1% PE1 was improved
when retorted at 123°C and 127°C for 30 to 60 minutes, when
compared to the initial process conditions (at 127°C for 17
minutes).