Abdul Rahman, R.

Ghazali, H. M.

Yusof, S.

Universiti Putra Malaysia Institutional Repository

UPM Research Report 1998: Volume 2EFFECT OF HEAT TREATMENT IN PREVENTINGBROWNING IN SUGARCANE JUICES. Yusof, H.M. Ghazali and R.A. RahmanFaculty Food Science & BiotechrwlogyUniversiti Putra Malaysia, 43400 UPM, Serdang, Selangor,MalaysiaKeywords: sugarcane juice, storage, quality, brown-ing, prevention.IntroductionFresh sugarcane juice is a popular beverage in Malaysia. Itsunique flavour and sweet taste makes a very thirst quenchingdrink especially when consume chilled. However, as reportedby Sharma et al. (1989) sugarcane juice is highly perishable.A short time lag between extraction and consumption cancause its sensory properties namely colour, flavour and vis-cosity to change. The colour of the juice will graduallychange from yellowish green to dark green and upon longerstorage it will become brownish green. The colour change isoften accompanied by change in flavour and taste, fromsweet to an objectionably sourish taste. Buchelli and Robin-son (1994) suggested that enzymatic browning was the majorcause for the change in colour of fresh sugarcane juice. Theenzyme responsible for enzymatic browning reaction hasbeen referred to as polyphenoloxidase (PPO). Pasteurisationor conventional heat treatment of sugarcane juice is impracti-cal since it would also cause nonenzymatic browning of thejuice and at the same time impart a jaggery taste. The objec-tive of this project was to study the effects of blanchingtreatment of the canes on juice quality as well as to deter-mine the suitable time and temperature combination for theblanching treatment.Materials and MethodsSugarcane of the yellow variety was used in this study. Itssupply was obtained from a farm in Semenyih. They wereharvested at commercial maturity stage, approximately 8months old. Upon arrival at the laboratory, they werecleaned, washed and cut into 3ft. lengths. The canes werethen subjected to different blanching treatments: A) Waterblanching i) at 75°C for 11,12,13 and 14min. ii). At 80°C for11,12,13, and 14 min. iii) at 85°C for 11, 12, 13 and 14 min;and B). Steam blanching at 100°C for 11, 12, 13 and 14 min.After the blanching treatments the canes were immediatelycooled in ice water before extracting the juice. Sugarcanejuice was extracted using a three roller power machinecrusher, filtered and stored at 4°C before quality analysiswere done. The quality parameters examined on the extractedjuice were colour using the Hunter colour difference meter,PPO enzyme activity (Augustine et al. 1985), chlorophyll(Richard and Thompson, 1952) and sensory evaluation todetect the difference and preference for colour and taste ofthe treated samples.Results and DiscussionColour. The colour of sugarcane juice was monitored by re-cording its 'L' Lightness, '-a' greenness and 'b' yellownessvalues. It was apparent that both prolonged time of heatingat a particular temperature as well as increasing the heatingtemperatures decreased the 'L', 'a' and 'b' values of the ex-tracted juice. The decrease in 'L' value indicated that thejuice was getting darker while the decrease in alb valueshowed that the juice was becoming more yellow than green.182In addition, the 'L', 'a' and 'b' values of juices extractedfrom canes that were blanched at 75, 80 and 85°C further de-creased during storage at 5°C. The colour of the juices wasobserved to be brown. In contrast, the canes that wereblanched at 100°C for 13 mins. did not develop any browncolour during storage. This indicated that blanching treat-ment had positive effects in preventing browning of sugar-cane juice.Enzyme activity: From the enzyme heat inactivation trials itwas observed that low temperature heat treatment was notable to inhibit the enzyme activity. Heating the canes to aninternal temperature of 100°C for 12-13 min managed tocompletely inactivate the enzymeChlorophyll: Chlorophyll was observed to contribute to theattractive colour of sugarcane juice. Results of this study in-dicated that blanching treatment reduced the total chlorophyllcontent of sugarcane juice. The higher the temperature andthe longer the blanching time the greater was the amount re-duced. This was in concomitant with the decrease in alb val-ues recorded above. The initial chlorophyll content was250f.l.gIliter.Blanching of canes at 75, 80, 85 and 100°C re-duced the contents to 120, 89, 68 and 52f.l.gIliterespectively.These values decreased further after a 12-hour storage at5°C, perhaps due to the formation of dull, olive brown pheo-phytin (Jeanna, 1991) which contributed to the change frombright greenish to brownish colour.Sensory evaluation: Results of panellists evaluation on thecolour of sugarcane juice extracted from canes that wereblanched at different times and temperatures showed therewere no significant difference in the colour. However, com-paring among products of the four temperature regimes, thecolour of juice extracted from canes blanched at 100°C for13 min was most preferred. For taste the canes that wereblanched at 100°C for 12min produced better tasting juice.ConclusionsSeveral factors were involved in the loss of colour of sugar-cane juice but the activity of the enzyme polyphenoloxidaseand chlorophyll degradation were major factors. Blanchingof canes helped to inactivate the enzyme. No intense brown-ing was observed in cane juice extracted from blanchedcanes. Steam blanching was more feasible compared to wa-ter blanching. The optimum temperature and time forblanching of canes was 100°C for 12-13 mins.ReferencesAugustine, M.A., Ghazali, H.M. and Hashim, H. 1985. Polyphe-noloxidese from guava (Psidium guajava L). J. Sci. Food Agric.36,1259-1265.Buchelli, C.S. and Robinson, S.P. 1994. Contribution of enzymaticbrowning in the colour of sugarcane juice. J.Agric.Food Chem.42: 257-261.Jeanna, G. 1991. Chlorophyll pigments in vegetables. Van NostrandReinhold Publication.Richard, F.A. and Thompson, T.G. 1952. The estimation and char-acterisation of plankton populations by pigment analysis. ii.Spectrophotometric method for the estimation of plankton pig-ments. J. Mar. Res. 11(2): 156.Sharma, K.P., Ratan, B.K. and Kanwar, R.S. 1989. Improvement insugar recovery by preventing bacterial polysaccharide productionin cane sugar., Bhartya Sugar. 14: 15-18.Supported by IRPA Grant O/-{)2-04-O126

Effect of heat treatment in preventing browning in sugarcane juice

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Effect of heat treatment in preventing browning in sugarcane juice

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