Effects of heat processing on product quality of sous-vide broccoli packs

Effects of heat processing on product quality of sous-vide broccoli packs. by Nicolaas Hugo Vlok Thesis submitted in part fulfilment of the require...
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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.

4.3

Analyses

4.3.1

pH-analysis

The significantly greater (P

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