Effects of heat processing on product quality of sous-vide broccoli packs.
by
Nicolaas Hugo Vlok
Thesis submitted in part fulfilment of the requirements for the degree
Magister Technologiae: Food Technology in the Department: Food Technology & Manufacture, School of Mechanical and Process Engineering, at the Cape Technikon.
Date of submission:
Project supervisor:
January 1998
H B van der Merwe
Summary
To establish the optimum pasteurisation procedure, the effects of sous-vide heat processing on the pH, ascorbic acid and sensory aspects of broccoli (Brassica oleracea var.
Italica) were studied.
Broccoli
florets
were
blanched
using
steam
and
ammonia(NH 3 )-steam, chilled to O.05) during the 21 day storage period at 2° 4°C (Fig.3.1/Annexure 3.3).
NH 3 -steam-blanched broccoli, on the other hand, showed a signiricant (PO.05)
58
CHAPTER 4 DISCUSSION
4.1
Heat penetration measurement
The first trials indicated that particular attention has to be paid to the packing gland integrity, as some of the bags lost their vacuum due to leaks at the packing gland. and no analyses
could
aggravated
be
during
carried the
out.
insertion
This
problem
procedure
was
of
the
thermocouple into its correct position. Precautionary steps were successfully introduced to overcome the problem by using a special heavy duty tape. Tesa Multikrafttape. able to withstand the processing conditions and mechanical strains. A section of tape was adhered to the outside of the bag over the area where the hole for the packing gland was to be made. This ensured a very strong bonding to the bag material. which permitted the successful insertion of the thermocouple without losing vacuum. The tape solved the problem and no further leaks were observed.
4.2
Pasteurisation
Pasteurisation temperatures of 73 0
up to 85°C in 3°C
intervals were chosen to test the
possible
temperature on the various quality aspects.
effects
of
while at the
59
same
time
investigating
the
practicality
of
reducing
processing time by using higher temperatures. As the reference temperature was 70
D
e,
temperatures higher than
70 D e were selected in order to reduce pasteurisation time.
The study was successful in showing the significance of the various treatments from an overall quality perspective. In terms of optimising a sous-vide broccoli process, the· first objective was to use quality raw materials.
Secondly,
broccoli was exposed to the same conditions prior and during the processing for all trials. However,
being a
natural product, certain aspects are impossible to dictate and therefore may influence the final product quality. For that reason all samples prepared for any replicate of the various analyses were cut from the same broccoli head. This procedure ensured reproducibility and assisted in showing that it is possible to predict quality aspects based on the effects of heat on the broccoli.