method, it was chosen to let the respective companies carry out the
sensorial tests themselves, because it is believed that they know the
sensorial properties of their own product best and they can make a
reliable judgment.
For rumpsteak and grated cheese the analysis was performed by a
taste panel of six persons. These persons were untrained company
staff (e.g., quality managers). It was examined to what extent a difference
could be observed between a sample packed in the reference and
(a) sample(s) packed in the biobased packaging for seven parameters:
look, color, odor, texture, mouthfeel, flavor and tastiness. Each panelist
was given two samples (one fromeach of the different packagingmaterials)
for rumpsteak or three samples (one from each of the different
packaging materials) for grated cheese at the same time. Panelists
scored (1 to 10) each sample separately for every parameter and an
average and standard deviation of these scores was calculated. The
sensory evaluation for ham sausage and filet de saxe was performed
by a taste panel of ±30 persons (untrained company staff) by means
of a triangle test. It was examined if panelist could detect a difference
between the samples (packed in the different materials) and which
sample was preferred, for three parameters: odor, color and flavor.
Each panelist tasted these samples from left to right. The results of this
analysis were statistically processed (Roessler, one tailed). For French
fries the analysis was performed by a taste panel of three or four
company experts. For French fries, look, color, odor and feeling before
baking were looked at and on the first day of analysis (day 16) also
look, color, feeling and flavor after baking were evaluated. A general
opinion (+ or -) was given for each tested parameter.
2.4.7. Performance in industrial environment
The introduction of good functional bioplastics as a packaging
material on industrial scale can only be successful if these materials
can be handled on industrial packaging machines. Therefore, several
films were selected to be tested on industrial packaging lines (vertical
and horizontal flow pack machines) at different food companies. The
seal properties and the speed of the machine were altered to make
good sealed packages. As stated previously, it is of utmost importance
that the applied gas atmosphere is maintained in the headspace of the
packaging during storage. Therefore, the ability to make good sealed
packages is very important when food products are MAP-packed,
since leaks in the package can counteract the carefully selected barrier
properties of the film. These tests were performed for French fries,
ham sausage and Strasbourg (sliced meat product). In case good sealed
packages could be made, gas analysis on these packages were
performed during the shelf-life.
3. Results and discussion
Parameters with a constant value throughout the shelf-life are not
shown.
3.1. Short shelf-life products (laboratory-scale)
For rumpsteak, the minimum O2 concentration in the packaging
necessary for color retention was stipulated at 60% and the minimum
CO2 concentration for a maximum of antimicrobial activity at 20%
(limits of the industrial partners). In Fig. 1 it can be seen that a combination
of the PLA tray with Natureflex™N913/PLA as a topfilm had,
although the oxygen level was slightly lower than in the reference
package, still sufficient barrier to keep the oxygen level in the package
above 60% and the CO2 concentration above 20% during the entire
shelf-life. This also explains the similarmicrobiological growth detected
in the biobased and the conventional packaging materials (Fig. 2) as
well as the similar pH. The latter remained constant at values 5.5–5.6
(data not shown). Also the aw-values remained constant for both
packages at values around 0.99 (data not shown).
Fig. 2 shows a similar trend for both packages for respectively the
total psychrotolerant aerobic plate count and the amount of psychrotolerant
lactic acid bacteria. For both parameters the maximum value
of 107 CFU/g is not exceeded during the shelf-life of rumpsteak. It can
also be stated that microbial spoilage will almost be completely caused
by psychrotolerant lactic acid bacteria, which means that the rejection
of the product should be based on sensorial evaluation (Uyttendaele,
Jacxsens, De Loy-Hendrickx, Devlieghere, & Debevere, 2010). Assuming
that in a tray/lidding filmcombination for cold storage, the tray achieves
appropriate gas-barrier properties through its thickness independent of
the material, the material of the much thinner lidding film will determine
the barrier properties of the total packaging concept. Nevertheless
the fact that the gas-barrier properties of the conventional packaging
were better (PET/CPP; see Table 2) compared to the biobased packaging
(cellulose/PLA; see Table 2), the barrier properties of the latterwere still
sufficient to provide the desired shelf-life. The amount of yeasts and
molds remained under the detection limit (b2 log CFU/g) during the
entire storage period and are not shown.
From Fig. 3 it can be deducted thatmore loss of red color (parameter
a*) occurs when rumpsteak is packed in the PLA tray + Natureflex
™N913/PLA package in comparison with the reference package.
Especially on day 6 and day 8 this difference was clearly observed. It
should be noted that big variations in color were observed between
different samples in the same packaging material. According to Young
and West (2001) the uneven color of meat cuts is normal and due to
marbling and uneven discoloration. Uneven discoloration is probably
caused by surface variation in myoglobin redox state (Mancini &
Hunt, 2005). This iswhy instrumental data should be correlated to visual
judgment (sensorial evaluation).
The results of the sensory evaluation (data not shown) showed that
the bio-packaging scored better on mouthfeel (7.1 vs 6.2), but scored
less well on color (6 vs 7.1). The other tested parameters had the
same score for both packages. Despite the big variation in color within
the same packaging material, the sensory evaluation confirms the
results of the color measurements. So, from both the color measurements
and the sensory evaluation it was clear that the bio-packaging
had a negative effect on the red color, leading to a less attractive
product. Since only a small difference in headspace oxygen concentration
was observed between the biobased and the reference packaging,
the residual oxygen was always above 60% and a similar microbial
growth was observed, the negative effect on color can most likely be
attributed to different light-transparency properties of the packaging
materials. Therefore, the transparencies of the different materials were
further investigated (see Section 3.3).
3.2