prepared
by firstly dissolving the CMC (0.2% w/w) in a water–ethanol
mixture (4:1 v/v) under magnetic stirring at 60 C and then adding
the plasticizer PEG (0.1% w/w) and the sucrose fatty acid ester F-50
(0.8% w/w), followed by stirring for 1 h. Two different coatings
using the whey protein isolate were prepared; WPI 1 and WPI 2,
which included 4% w/w WPI and 1% w/w sorbitol as a plasticizer,
both dissolved in distilled water. The solutions were denatured
for 30 min in a 90 C water bath under continuous shaking and
then were rapidly cooled in an ice bath, in order to stop further
protein denaturation, and finally equilibrated to room temperature.
WPI 2 also included 1% w/w stearic acid as a lipid constituent,
which was incorporated to the coating solution just after the denaturation
step by homogenization at 19,000 rpm for 4 min using an
UltraTurrax T25 homogenizer (IKA Labortechnik, Staufen, Germany).
The pullulan based coating solution (P) was obtained by
dissolving pullulan (5% w/w) in distilled water under magnetic
stirring at 60 C with subsequent addition of sorbitol (1% w/w)
and a sucrose fatty acid ester F-50 (1% w/w), followed by stirring
for 1 h. All the coating solutions were left overnight at 4 C in order
to eliminate air bubbles. The composition of the coatings used in
this work was selected among a large number of other coatings
examined in preliminary trials.
Coating was carried out at room temperature by dipping the
asparagus spears for 30 s in the formulated suspensions and then
slow drying at ambient conditions, by turning them from time to
time, for about 2 h. After the coating treatment the samples were
placed in plastic trays and subjected to cold storage