Title page for ETD etd-07252012-105148


Document Type Master's Dissertation
Author Nleya, Kathleen Mutsa
Email kathleennleya@gmail.com
URN etd-07252012-105148
Document Title Relating physico-chemical properties of frozen green peas (Pisum sativum L.) with sensory quality
Degree MSc
Department Food Science
Supervisor
Advisor Name Title
Prof A Minnaar Co-Supervisor
Prof H L De Kock Supervisor
Keywords
  • physico-chemical properties
  • sensory quality
  • frozen green peas
  • Pisum sativum L.
Date 2012-04-24
Availability unrestricted
Abstract
Green garden peas (Pisum sativum L.) are a popular vegetable used in meal preparation worldwide. Green peas are commonly available in their frozen form due to their short growing season. Green peas are easily susceptible to changes in the field, immediately after harvest, during processing and storage, and thereforerequire careful handling to maintain good quality. The acceptability of frozen green peas is greatly dependent on the sensory quality. Descriptive sensory profiles and physico-chemical properties of frozen green peas can be investigated and used to assess and explain product quality.

Six brands of frozen green peas representing product sold for retail and caterer's markets were purchased and subjected to descriptive sensory evaluation, physico-chemical analyses and quality grading. Four batches with different best before dates were purchased for each brand. Quality grading was done using statutory standards and a selected company protocol. Dry matter content, alcohol insoluble solids content, starch content, °Brix, residual peroxidase activity, size sorting, hardness using texture analysis and colour measurements were carried out for physico-chemical analyses.

Generally, retail class peas were of superior sensory quality to caterer's peas although one caterer's brand had quality traits that were more comparable with the retail brands than the other caterer's brands. Quality grading revealed that frozen green peas can be downgraded due to poor colour, presence of extraneous vegetable matter, presence of sandy grits and soil stains, poor flavour and poor texture. Downgrading of peas can be due to one reason or due to a combination of two or more poor quality characteristics. Good quality peas were described as sweeter, smaller, greener, more moist and more tender than the poorer quality peas usingdescriptive sensory evaluation. Good peas also had high °Brix content, more intense green colour, low starch, alcohol insoluble solids, dry matter contents and texture hardness measured. Quality grading revealed that flavour problems were the major cause for low graded samples. Sensory evaluation and the methods used for instrumental analyses however, showed more easily the variations in texture attributes than flavour attributes of peas.

Poor flavour was probably caused by ineffective blanching, low soluble solids content which enhanced the perception of bitterness and the presence of acetone notes. Poorly coloured peas were also either underblanched or had low moisture contents. Mealiness and hardness in peas were explained by high starch, alcohol insoluble solids and dry matter contents. Instrumental texture analysis showed indications that the harder peas also had tougher skins in addition to harder cotyledons. Lower peas also displayed characteristics typical of delayed harvesting and post-processing temperature abuse such as dehydration and pale green/white colouration.

The sensory quality of frozen green peas can be predicted from the physico-chemical methods of analysis used in this study. Some of the frozen peas on sale are below the acceptable standards of quality. To achieve good frozen pea quality it is important to put emphasis on maturity at harvest and post processing storage conditions (store at -18 °C or lower and avoidfluctuatingtemperatures). The use of a strict quality grading scheme has been shownto result in good quality frozen peas.

Copyright © 2011, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Nleya, KM 2011, Relating physico-chemical properties of frozen green peas (Pisum sativum L.) with sensory quality, MSc dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-07252012-105148 / >

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