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Relationship of Maturity as Indicated by Flesh Color to Quality of Canned Clingstone Peaches
Relationship of Maturity as Indicated by Flesh Color to Quality of Canned Clingstone Peaches T. Fuleki and Frances I. Cook Horticultural Products Laboratory Horticultural Research Institute of Ontario Ontario Ministry of Agriculture and Food Vineland Station, Ontario, LOR 2EO
Abstract Clingstone peaches (cultivars Babygold 5 and 7) ranging in maturity from unripe to over-ripe were classified according to flesh color into 10 maturity groups, using a Hunterlab D25P Color Difference Meter. The canned peach halves were graded on the basis of color. texture and flavor by an expert panel. Maturity affected the quality of the canned peach halves. Canning improved the color of unripe peaches. The maturity groups giving the best quality canned products were those with Hunter al, readings of 4.0 to 6.0 for the raw flesh color of Babygold 5 and 10.0 to 12.0 for that of Babygold 7. The average drained weight of canned halves of the less mature peaches was lower than that of the more mature.
Resume Les varietes de peches de type Pavie (Babygold 5 et 7) furent classes selon la couleur de chair en 10 groupes de maturite s'echelonnant de fruits verts a trop murs, en utilisant un appareil colorimetrique "Hunterlab D25P Color Difference Meter". Les moities de peches en conserve furent classees par un groupe d'experts selon la couleur, la texture, et la saveur. La maturite des peches affecta la qualite en conserve. La mise en conserve ameliora la couleur des fruits verts. Les classes de maturite donnantla meilleur qualite de conserve furent celles ayant une lecture "Hunter al," de 4.0 a 6.0 pour la chair fraiche de Babygold 5 et une lecture de 10.0 a 12.0 pour celie de Babygold 7. Le poid egoutte moyen des moities de peches les moins mures etait moindre que celui des plus mures.
Introduction Clingstone peaches must be picked at the proper maturity for a high quality canned product (Leonard, et al., 1953). Unlike freestone peaches, the maturity of clingstone peaches cannot readily be determined on the basis of texture or skin color. However, the flesh color of clingstone peach changes from green to orange-yellow during ripening. This flesh color change is used in California (Anon., 1966; Claypool, 1966) to determine maturity and grade of clingstone peach for canning. The disappearance of chlorophyll and accumulation of carotenoids are responsible for the color change during ripening. The flesh color of the ripe fruit depends on the concentration and type of major carotenoid pigments present (Dei-Tutu et al., 1970). Commercial canning of clingstone peaches, (other than for baby food), started in Ontario in 1969. The proper ptcktng maturity for them has not yet been established. Following a request by growers and processors, the relatIonship between maturity, as measured by the color of raw .peach flesh, and quality of the canned product was studIed.
Material and Methods Peach samples , . Babygold 5 and Babygold 7, the two clingstone peach ~ultlvars most widely grown in Ontario, were obtained f rom the Horticultural Research Institute of Ontario and a 10c~1 processor during the 1970 season. The fruits were usually processed without delay. Some of medium maturIty were further ripened to provide sufficient quantities of over-rIpe peaches. 43
Color measurement on the raw peaches The flesh was exposed on the small side of the peach by making a flat cut on a line parallel to the suture. The. cut was made by removing two 3 mm slices with a modi. fied Berkel 1500 meat slicer. The slices were discarded and the remaining portion of the fruit was used for color meas. urement and canning. The reflected color of the peach flesh was measured with the "P" optical head of a Hunt. erlab D25 Color and Color Difference Meter (Hunter As· sociates Lab. Inc., Fairfax, Va.) as described in an earlier communication (Fuleki, 1971). Since the Hunter at. value gave the best correlation (r = 0.950) with visual assess,; ment of raw peach flesh color (Fuleki, 1971), this was usedfor the color sorting of peaches. Each peach was placed on the basis of its flesh color into one of the following matu· rity groups (from unripe to over-ripe): Below -2, -2 to 0, o to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, 10 to 12, 12 to 14, and above 14 at.. To have full, uncut halves for evaluation of the canned product, the small side was used for color measurement and the large side was canned. Canning The peaches were halved and pitted by hand. The halves previously cut for color measurement were discarded. The uncut halves were peeled by dipping in a 1% solution of sodium hydroxide at 98°C for 75 seconds followed by a cold water spray to remove peel and excess lye. The peeled halves were rinsed again, first in dilute acid. solution and then in water. They were then placed into 19 oz cans and covered with 45% sugar syrup. The filleq cans were heated to 82°C, closed, cooked at 100°C for 15 min, and cooled immediately in cold running water. Sensory evaluation of the canned peaches The cans, within cultivars, were randomized and opened just before evaluation. The drained weight and the l number of halves in each can were recorded. The content of each can was placed on a white mat plastic-coated paper plate and presented to the judges for grading. ' Every can was evaluated once by each of 3 government inspectors and 3 experts from industry. Grading for color, texture and flavor were done separately and in that order. A 1 to 4 scale was used where the scores corresponded to the commercial grades of "Fancy", "Choice", "Standard" and "Substandard". The color grading was carried out in the Color Panel Room (Fuleki, 1971) under controlled illumination (7500 0 K). Only color was taken into consideration and the other appearance factors such as uniformity of color, size, freedom from blemishes and trimming were disregarded. After all judges finished the color grading on a lot, the samples were moved to another room to evaluate their texture and flavor under subdued illumination. J. Inst. Can. Sci. Technol. Aliment. Vol. 9. No. I. 1976
Table I. Reliability index of the six judges grading canned clingstone peaches.* Reliability index
Total scores _ for the judges
Judges Quality attributes Color Texture Flavor
Alpha reliability 0.95 0.62 0.84
2 0.72 0.31 0.52
0.75 0.34 0.62
4
5
6
0.66 0.3\ 0.47
0.62 0.30 0.49
0.69 0.36 0.63
3 0.71 0.19 0.34
Mean**S.D. 9.59 7.60 8.85
4.-16 1.82 3.07
* Number of cans = 340. ** The minimum and maximum total mean scores would be 6 and 24 respectively.
Table 2. Relation between maturity. as indicated by raw flesh color and quality of canned
~Iingstone
peaches.
Babygold 5 Maturity group'
Avga.. reading'
Below-2 2-toO Ot02 2t04 4t06 6to 8 8to 10 10 to 12 12to 14 Above 14 C.V.(%)3
-3.2 -0.7 1.1 2.9 5.0 7.0 8.7 10.8 12.9
No. of cans 2 4 16 19 24 19 16 4 I
Babygold 7 Canned quality-Avg score' Color
Texture
Flavor
3.0 1.9 1.5 1.4
1.8 1.5
1.9 1.5 1.2
1.2 1.1 1.1 1.4 1.3
1.2 1.2 1.1 1.3 1.3 1.5 1.3
1.2 1.6 1.5 2.1 1.6
24.0
15.0
27.0
1.3
Avga .. reading'
No. of cans
-3.8 -1.0 1.0 2.9 5.0 7.0 9.0 10.9 12.8 15.0
16 22 21 19 17 21 30 28 20 6
Canned quality-Avg score' Color
Texture
Flavor
3.1 2.6 2.1 1.9 1.4 1.2 1.2 1.1 1.1 1.3 21.0
1.2
1.8 1.4 1.3 1.4 1.3
1.2 1.1 1.2 1.2 1.2 1.2 1.1 1.2 1.3 16.3
1.3 1.3 1.2 1.3 1.3 22.6
Raw flesh color measured by the Hunter a .. reading was used as maturity index. The disappearance of greenish color and increasing maturity was indicated by higher a.. value. 'Grading was done on a I to 4 scale. 1 being the best score. "Degrees of freedom for error: Babygold 5 = 95: Babygold 7 = 189. 1
The reliability of the judges was assessed by item analysis using the color, texture and flavor scores given by each of the judges (Kerlinger, 1973). The reliability index of each judge and the whole panel (alpha reliability) are presented in Table I. The panel exhibited the highest r~liability judging color, the sensory quality in which the difference between samples was the most pronounced. The alph~ reliability decreased as the variability in the judged qualIty factor between cans became smaller. The overall reliability of every judge was sufficiently high for inclusion of their scores in the results. Color measurement on the canned peaches After grading, a sufficient quantity remained (avg. 240 g) from most samples for instrumental color measurement. The peaches were drained and macerated in a Waring Blendor. The macerate was poured into a 12.7 x 12.7 x 5.1 em plexiglass sample cell, placed in a desiccator and deaerated by vacuum treatment. The color was measured through the optically clear bottom of the sample cell on tDh~ "L" optical head of a Hunterlab 025 Color and Color Ifference Meter. To compare the color of canned peaches to that of the haw fruit, the Hunter values obtained on the "L" optical "e~d were transformed to the corresponding values on the ~ head, using the regression equations established for t IS purpose: L (for P head) = -4,197836 + 0.959114.L (for L head) abl. (for P head) ~ 2.398122 + 0.521519.al. (for L head) I. (for P head) = -0.245395 + 0.799950.bl. (for L head)
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Can. Insl. Food Sci. Technol. J. Vol. 8. No.4.
1975
The coefficient of variability (Steel and Torrie, 1960) was calculated for the color, texture and flavor scores.
Results and Discussion Raw flesh color and canned fruit quality Table 2 presents the results of the grading of the canned peaches processed at different stages of maturity. The results show a definite relationship between maturity and canned fruit quality. Immature fruit gave a poor quality product. Color was the limiting factor at low maturities. The best quality product was obtained by canning peaches which gave average Hunter a L readings of 5.0 for Babygold 5 and 10.9 for Babygold 7. The texture and flavor declined somewhat when over-mature fruit was canned. The deterioration of flavor was particularly pronounced in the Babygold 5 cultivar. The Hunter a L values for the raw and canned peaches (Tables 3 and 4) indicate that the color of the immature peaches improved upon canning. A similar improvement in color was reported by Leonard et al. (1961). They attributed it to the d~struction of chlorophyll during heat sterilization. The increase in hue value (taw' a,/bl.) which occurred in the unripe samples (Tables 3 and 4) supports this theory. The canned product also had a darker color as indicated by the lower L reading and saturation value [ (a L " + bl."Wl than the corresponding raw peaches. This suggests that infiltration of the intercellular airspaces by the syrup upon canning was also important in the improvement of color.
44
Table 3. Changes in color due to canning in Babygold 5 clingstone peaches processed at different maturities.
Maturity group' -2toO o to 2 2 t04 4 to 6 6 to 8 8 to 10 10 to 12
No. of samples measured Fresh Canned 27 103 143 179 196 102 27
4 16 19 23 18 16 4
Average Hunter reading'
Fresh
L Canned
Fresh
al. Canned
Fresh
72.9 73.2 72.5 72.0 71.2 69.9 68.9
55.1 54.8 55.9 55.9 56.7 56.6 56.0
-0.7 1.1 2.9 5.0 7.0 8.7 10.8
6.3 7.0 7.4 7.7 8.3 8.7 9.5
39.0 39.3 39.6 39.3 38.7 38.4 38.0
bl. Canned
Hue' Fresh Canned
a,/L" Fresh Canned
27.9 -0.0096 0.015 27.9 0.040 28.4 0.069 28.7 0.098 28.9 0.12 29.2 0.16 29.0
12.8 14.0 14.5 15.1 16.1 16.6 18.2
-1.0
0.12 0.13 0.13 0.14 0.15 0.15 0.17
Saturation Fresh Canned
1.3
4.2 7.4 10.2 12.9 15.7
39.0 39.3 39.7 39.2 39.3 39.4 39.5
28.5 28.7 29.3 30.2 30.1 30.5 30.5
, Raw flesh color measured by the Hunter al. reading was used as maturity index. The disappearance of greenish color and increasing maturity was indicated by higher a L value. . , The "fresh" values refer to readings taken on individual raw peach halves while those of the "canned" to whole cans. , Color index used by Dei-Tutu et al. (1970). , Hue was calculated as tan" a,/bl.' The hue angle increases as it changes from pale-green to orange-yellow. ., Saturation was calculated as (aI.' + bt.,),n. It is proportional to the strength of color. Table 4. Changes in color due to canning in Babygold 7 Clingstone peaches processed at different maturities. Average Hunter reading' No. of samples measured Maturity group' Below -2 .............. -2 toO ................... o to 2...................... 2 to 4...................... 4 to 6...................... 6 to 8...................... 8 to 10.................... 10 to 12.................. 12 to 14.................. Above 14 ...............
Fresh Canned 154 129 139 152 126 159 235 248 125 35
16 22 21 19 17 21 30 28 20 6
Fresh Canned 71.9 72.6 72.9 73.5 73.6 73.9 74.1 72.8 71.6 70.6
48.0 50.3 50.7 51.4 52.1 53.4 54.4 54.0 53.0 52.4
Fresh Canned -3.8 -1.0 1.0 2.9 5.0 7.0 9.0 10.9 12.8 15.0
4.5 5.2 5.9 6.3 7.2 7.7 8.2 9.0 9.5 9.6
Hue'
bl.
al./L'
Fresh Canned
Fresh Canned
al.
36.9 38.0 38.2 38.8 38.9 38.6 38.1 38.1 38.1 38.0
24.9 26.1 26.5 26.9 27.5 28.5 28.5 28.9 28.2 27.8
-0.053 -0.014 0.014 0.039 0.068 0.095 0.12 0.15 0.18 0.21
0.095 0.10 0.12 0.12 0.14 0.14 0.15 0.17 0.18 0.19
Saturation:'
Fresh Canned -5.7 -1.5 1.5 4.3 7.4 10.2 13.5 16.2 18.8 21.3
10.4 11.2 12.6 13.3 14.6 15.4 16.1 17.6 18.5 19.1
Fresh
Canneil
36.7 38.0 38.2 38.9 39.2 39.2 39.2 39.5 40.2 40.9
25.3 26.7 27.1 27.6 28.4 29.5 29.6 30.3 29.8 29.4
'Raw flesh color measured by the Hunter al. reading prior to canning was used as maturity index. The disappearance of greenish color and increasing maturity was indicated by a higher al. value. 'The "fresh" values refer to readings taken on individual raw peach halves while those of the "canned" to whole cans. 'Color index used by Dei-Tutu et al. (1970) I Hue was calculated as tan" a,/bl.' The hue angle increases as it changes from pale-green to orange-yellow. "'Saturation was calculated as (at.' + bt.'),n. It is proportional to the strength of color.
Maturity and yield Previous work at the Horticultural Research Institute of Ontario (Upshall, 1943) demonstrated that premature freestone peaches were smaller than mature ones. To investigate the relationship between maturity and fruit size, the average drained weight of the canned halves for each maturity group was recorded (Table 5). The peaches in the 2 to 4 maturity group had almost reached their full size. Howeve.r, less mature peaches were considerably smaller. Haryestmg before that stage of maturity would result in slgmficantly lower yield for the grower.
Conclusions The results showed that flesh color is a good index of for Ontario-grown clingstone peaches. The flesh ~olor of raw peaches could be reliably measured by Hunter ~ values USll~g a Hunterlab Color and Color Difference th:ter. Matunty affected the color, flavor and texture, in th ~t order, of the canned peach halves. Canning improved ~ ~olor, particularly with fruit not fully mature. The best ljua tty canned products were obtained from fruit with ~atunty
45
Table 5. Drained weight of canned peach halves processed at different maturities within 24 hours of harvest. _B_a_b.:...y:::.go_l_d_5
Below -2 -2 toO Ot02 2 t04 4t06 6 t08 8 to 10
-...:B:....:a-...:b.:'..yE.go:....:l_d_7_~ I
Maturity group I
i
Avg wt per half, g , 49.3 56.0 51.6 66.4 68.9 64.0 78.9
54.4 60.1 63.9 71.0 71.5 76.7 73.4
, Raw flesh color measured by the Hunter al. reading was used as malUrity index. The disappearance of greenish color and increasing malUrtlY' is indicated by higher at. value. Larger sides of the peaches were canned.
Hunter a L readings of 4.0 to 6.0 in the case of Babygold 5 and 10.0 to 12.0 in the case of Babygold 7. Picking imma' ture fruits would reduce the yield as well as lower the qual' ity of the canned product. J. Insl. Can. Sci. Technol. Aliment Vol. 8. No.4. 191'
l.4ckDowledgements The authors are indebted to Dr. G. C. Ashton, Dr. I. McMillan and Mrs. Jeanette Hines, University of Guelph, Guelph for statistical advice and computer analysis of the data. W. R. Breckenridge, J. F. Mott, N. G. Pearson and VI Routby, Canada Department of Agriculture, Fruit and v~getable Inspection Service; .0. qement and H.. Holt, eanadian Canners Ltd., HamIlton; B. Roberts, NIagara Food Products Ltd., Stoney Creek, for their expert grading of the canned peaches; J. C. Rider, Canadian Canners Ltd., St. Catharines and O. A. Bradt for advice and supplying the peaches; Judith L. Allison, R. B. Palabay and other members of the Hor~icultural Pro.ducts ~aboratory staff of this Institute for theIr able techmcal assIstance.
..
Can.)nsl, Food Sci. Technol. J. Vol. 9, No. I, 1976
References Anon. 1966. Cling peach maturity study using Agtron instrument. Calif. Dept. Age.• Mimeo. 7 p. Claypool. L. L. 1966. Maturity indices for processing clings and freestones. In, Summary of the National Peach Conference. New Brunswick. N.J., March I J -12, 1965. 179. Dei-Tutu. J .. Edwards. R. A. and Buckle, K. A. 1970. Pigments and colour of Australian peach varieties. Food Techno!. Australia 22: 272. Fuleki. T. 1971. Methods for tristimulus colorimetry of apple. clingstone peach. tart cherry. tomaw juice and wine. HOft Res. Inst. of Ont Rep. for 1970: 137. Kerlinger, F. N. 1973. Foundations of Behaviourial Research. Holt, Rinehart and Winston, New York. Leonard, S. J.. Luh, B. S. and Hinreiner. E. 1953. Flavor evaluation of canned cling peaches. Food TechnoJ. 7:480. Leonard, S. J.. Luh, B. S.. Chichester. C. O. and Simone. M. 1961. Relationship of fresh clingstone peach color to color and grade after canning. Food Techno!. 15:492. Steel. R. G. D. and Torrie. J. H. 1960. Principles and Procedures of Statistics. McGraw-Hili, New York. Upshall. W. H. 1943. Increase in quantity. grade and returns from peaches as they approach opti· mum maturity. Sci. Agr. 23: 747.
Received June 27. 1975
46
Abstract Clingstone peaches (cultivars Babygold 5 and 7) ranging in maturity from unripe to over-ripe were classified according to flesh color into 10 maturity groups, using a Hunterlab D25P Color Difference Meter. The canned peach halves were graded on the basis of color. texture and flavor by an expert panel. Maturity affected the quality of the canned peach halves. Canning improved the color of unripe peaches. The maturity groups giving the best quality canned products were those with Hunter al, readings of 4.0 to 6.0 for the raw flesh color of Babygold 5 and 10.0 to 12.0 for that of Babygold 7. The average drained weight of canned halves of the less mature peaches was lower than that of the more mature.
Resume Les varietes de peches de type Pavie (Babygold 5 et 7) furent classes selon la couleur de chair en 10 groupes de maturite s'echelonnant de fruits verts a trop murs, en utilisant un appareil colorimetrique "Hunterlab D25P Color Difference Meter". Les moities de peches en conserve furent classees par un groupe d'experts selon la couleur, la texture, et la saveur. La maturite des peches affecta la qualite en conserve. La mise en conserve ameliora la couleur des fruits verts. Les classes de maturite donnantla meilleur qualite de conserve furent celles ayant une lecture "Hunter al," de 4.0 a 6.0 pour la chair fraiche de Babygold 5 et une lecture de 10.0 a 12.0 pour celie de Babygold 7. Le poid egoutte moyen des moities de peches les moins mures etait moindre que celui des plus mures.
Introduction Clingstone peaches must be picked at the proper maturity for a high quality canned product (Leonard, et al., 1953). Unlike freestone peaches, the maturity of clingstone peaches cannot readily be determined on the basis of texture or skin color. However, the flesh color of clingstone peach changes from green to orange-yellow during ripening. This flesh color change is used in California (Anon., 1966; Claypool, 1966) to determine maturity and grade of clingstone peach for canning. The disappearance of chlorophyll and accumulation of carotenoids are responsible for the color change during ripening. The flesh color of the ripe fruit depends on the concentration and type of major carotenoid pigments present (Dei-Tutu et al., 1970). Commercial canning of clingstone peaches, (other than for baby food), started in Ontario in 1969. The proper ptcktng maturity for them has not yet been established. Following a request by growers and processors, the relatIonship between maturity, as measured by the color of raw .peach flesh, and quality of the canned product was studIed.
Material and Methods Peach samples , . Babygold 5 and Babygold 7, the two clingstone peach ~ultlvars most widely grown in Ontario, were obtained f rom the Horticultural Research Institute of Ontario and a 10c~1 processor during the 1970 season. The fruits were usually processed without delay. Some of medium maturIty were further ripened to provide sufficient quantities of over-rIpe peaches. 43
Color measurement on the raw peaches The flesh was exposed on the small side of the peach by making a flat cut on a line parallel to the suture. The. cut was made by removing two 3 mm slices with a modi. fied Berkel 1500 meat slicer. The slices were discarded and the remaining portion of the fruit was used for color meas. urement and canning. The reflected color of the peach flesh was measured with the "P" optical head of a Hunt. erlab D25 Color and Color Difference Meter (Hunter As· sociates Lab. Inc., Fairfax, Va.) as described in an earlier communication (Fuleki, 1971). Since the Hunter at. value gave the best correlation (r = 0.950) with visual assess,; ment of raw peach flesh color (Fuleki, 1971), this was usedfor the color sorting of peaches. Each peach was placed on the basis of its flesh color into one of the following matu· rity groups (from unripe to over-ripe): Below -2, -2 to 0, o to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10, 10 to 12, 12 to 14, and above 14 at.. To have full, uncut halves for evaluation of the canned product, the small side was used for color measurement and the large side was canned. Canning The peaches were halved and pitted by hand. The halves previously cut for color measurement were discarded. The uncut halves were peeled by dipping in a 1% solution of sodium hydroxide at 98°C for 75 seconds followed by a cold water spray to remove peel and excess lye. The peeled halves were rinsed again, first in dilute acid. solution and then in water. They were then placed into 19 oz cans and covered with 45% sugar syrup. The filleq cans were heated to 82°C, closed, cooked at 100°C for 15 min, and cooled immediately in cold running water. Sensory evaluation of the canned peaches The cans, within cultivars, were randomized and opened just before evaluation. The drained weight and the l number of halves in each can were recorded. The content of each can was placed on a white mat plastic-coated paper plate and presented to the judges for grading. ' Every can was evaluated once by each of 3 government inspectors and 3 experts from industry. Grading for color, texture and flavor were done separately and in that order. A 1 to 4 scale was used where the scores corresponded to the commercial grades of "Fancy", "Choice", "Standard" and "Substandard". The color grading was carried out in the Color Panel Room (Fuleki, 1971) under controlled illumination (7500 0 K). Only color was taken into consideration and the other appearance factors such as uniformity of color, size, freedom from blemishes and trimming were disregarded. After all judges finished the color grading on a lot, the samples were moved to another room to evaluate their texture and flavor under subdued illumination. J. Inst. Can. Sci. Technol. Aliment. Vol. 9. No. I. 1976
Table I. Reliability index of the six judges grading canned clingstone peaches.* Reliability index
Total scores _ for the judges
Judges Quality attributes Color Texture Flavor
Alpha reliability 0.95 0.62 0.84
2 0.72 0.31 0.52
0.75 0.34 0.62
4
5
6
0.66 0.3\ 0.47
0.62 0.30 0.49
0.69 0.36 0.63
3 0.71 0.19 0.34
Mean**S.D. 9.59 7.60 8.85
4.-16 1.82 3.07
* Number of cans = 340. ** The minimum and maximum total mean scores would be 6 and 24 respectively.
Table 2. Relation between maturity. as indicated by raw flesh color and quality of canned
~Iingstone
peaches.
Babygold 5 Maturity group'
Avga.. reading'
Below-2 2-toO Ot02 2t04 4t06 6to 8 8to 10 10 to 12 12to 14 Above 14 C.V.(%)3
-3.2 -0.7 1.1 2.9 5.0 7.0 8.7 10.8 12.9
No. of cans 2 4 16 19 24 19 16 4 I
Babygold 7 Canned quality-Avg score' Color
Texture
Flavor
3.0 1.9 1.5 1.4
1.8 1.5
1.9 1.5 1.2
1.2 1.1 1.1 1.4 1.3
1.2 1.2 1.1 1.3 1.3 1.5 1.3
1.2 1.6 1.5 2.1 1.6
24.0
15.0
27.0
1.3
Avga .. reading'
No. of cans
-3.8 -1.0 1.0 2.9 5.0 7.0 9.0 10.9 12.8 15.0
16 22 21 19 17 21 30 28 20 6
Canned quality-Avg score' Color
Texture
Flavor
3.1 2.6 2.1 1.9 1.4 1.2 1.2 1.1 1.1 1.3 21.0
1.2
1.8 1.4 1.3 1.4 1.3
1.2 1.1 1.2 1.2 1.2 1.2 1.1 1.2 1.3 16.3
1.3 1.3 1.2 1.3 1.3 22.6
Raw flesh color measured by the Hunter a .. reading was used as maturity index. The disappearance of greenish color and increasing maturity was indicated by higher a.. value. 'Grading was done on a I to 4 scale. 1 being the best score. "Degrees of freedom for error: Babygold 5 = 95: Babygold 7 = 189. 1
The reliability of the judges was assessed by item analysis using the color, texture and flavor scores given by each of the judges (Kerlinger, 1973). The reliability index of each judge and the whole panel (alpha reliability) are presented in Table I. The panel exhibited the highest r~liability judging color, the sensory quality in which the difference between samples was the most pronounced. The alph~ reliability decreased as the variability in the judged qualIty factor between cans became smaller. The overall reliability of every judge was sufficiently high for inclusion of their scores in the results. Color measurement on the canned peaches After grading, a sufficient quantity remained (avg. 240 g) from most samples for instrumental color measurement. The peaches were drained and macerated in a Waring Blendor. The macerate was poured into a 12.7 x 12.7 x 5.1 em plexiglass sample cell, placed in a desiccator and deaerated by vacuum treatment. The color was measured through the optically clear bottom of the sample cell on tDh~ "L" optical head of a Hunterlab 025 Color and Color Ifference Meter. To compare the color of canned peaches to that of the haw fruit, the Hunter values obtained on the "L" optical "e~d were transformed to the corresponding values on the ~ head, using the regression equations established for t IS purpose: L (for P head) = -4,197836 + 0.959114.L (for L head) abl. (for P head) ~ 2.398122 + 0.521519.al. (for L head) I. (for P head) = -0.245395 + 0.799950.bl. (for L head)
h
Can. Insl. Food Sci. Technol. J. Vol. 8. No.4.
1975
The coefficient of variability (Steel and Torrie, 1960) was calculated for the color, texture and flavor scores.
Results and Discussion Raw flesh color and canned fruit quality Table 2 presents the results of the grading of the canned peaches processed at different stages of maturity. The results show a definite relationship between maturity and canned fruit quality. Immature fruit gave a poor quality product. Color was the limiting factor at low maturities. The best quality product was obtained by canning peaches which gave average Hunter a L readings of 5.0 for Babygold 5 and 10.9 for Babygold 7. The texture and flavor declined somewhat when over-mature fruit was canned. The deterioration of flavor was particularly pronounced in the Babygold 5 cultivar. The Hunter a L values for the raw and canned peaches (Tables 3 and 4) indicate that the color of the immature peaches improved upon canning. A similar improvement in color was reported by Leonard et al. (1961). They attributed it to the d~struction of chlorophyll during heat sterilization. The increase in hue value (taw' a,/bl.) which occurred in the unripe samples (Tables 3 and 4) supports this theory. The canned product also had a darker color as indicated by the lower L reading and saturation value [ (a L " + bl."Wl than the corresponding raw peaches. This suggests that infiltration of the intercellular airspaces by the syrup upon canning was also important in the improvement of color.
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Table 3. Changes in color due to canning in Babygold 5 clingstone peaches processed at different maturities.
Maturity group' -2toO o to 2 2 t04 4 to 6 6 to 8 8 to 10 10 to 12
No. of samples measured Fresh Canned 27 103 143 179 196 102 27
4 16 19 23 18 16 4
Average Hunter reading'
Fresh
L Canned
Fresh
al. Canned
Fresh
72.9 73.2 72.5 72.0 71.2 69.9 68.9
55.1 54.8 55.9 55.9 56.7 56.6 56.0
-0.7 1.1 2.9 5.0 7.0 8.7 10.8
6.3 7.0 7.4 7.7 8.3 8.7 9.5
39.0 39.3 39.6 39.3 38.7 38.4 38.0
bl. Canned
Hue' Fresh Canned
a,/L" Fresh Canned
27.9 -0.0096 0.015 27.9 0.040 28.4 0.069 28.7 0.098 28.9 0.12 29.2 0.16 29.0
12.8 14.0 14.5 15.1 16.1 16.6 18.2
-1.0
0.12 0.13 0.13 0.14 0.15 0.15 0.17
Saturation Fresh Canned
1.3
4.2 7.4 10.2 12.9 15.7
39.0 39.3 39.7 39.2 39.3 39.4 39.5
28.5 28.7 29.3 30.2 30.1 30.5 30.5
, Raw flesh color measured by the Hunter al. reading was used as maturity index. The disappearance of greenish color and increasing maturity was indicated by higher a L value. . , The "fresh" values refer to readings taken on individual raw peach halves while those of the "canned" to whole cans. , Color index used by Dei-Tutu et al. (1970). , Hue was calculated as tan" a,/bl.' The hue angle increases as it changes from pale-green to orange-yellow. ., Saturation was calculated as (aI.' + bt.,),n. It is proportional to the strength of color. Table 4. Changes in color due to canning in Babygold 7 Clingstone peaches processed at different maturities. Average Hunter reading' No. of samples measured Maturity group' Below -2 .............. -2 toO ................... o to 2...................... 2 to 4...................... 4 to 6...................... 6 to 8...................... 8 to 10.................... 10 to 12.................. 12 to 14.................. Above 14 ...............
Fresh Canned 154 129 139 152 126 159 235 248 125 35
16 22 21 19 17 21 30 28 20 6
Fresh Canned 71.9 72.6 72.9 73.5 73.6 73.9 74.1 72.8 71.6 70.6
48.0 50.3 50.7 51.4 52.1 53.4 54.4 54.0 53.0 52.4
Fresh Canned -3.8 -1.0 1.0 2.9 5.0 7.0 9.0 10.9 12.8 15.0
4.5 5.2 5.9 6.3 7.2 7.7 8.2 9.0 9.5 9.6
Hue'
bl.
al./L'
Fresh Canned
Fresh Canned
al.
36.9 38.0 38.2 38.8 38.9 38.6 38.1 38.1 38.1 38.0
24.9 26.1 26.5 26.9 27.5 28.5 28.5 28.9 28.2 27.8
-0.053 -0.014 0.014 0.039 0.068 0.095 0.12 0.15 0.18 0.21
0.095 0.10 0.12 0.12 0.14 0.14 0.15 0.17 0.18 0.19
Saturation:'
Fresh Canned -5.7 -1.5 1.5 4.3 7.4 10.2 13.5 16.2 18.8 21.3
10.4 11.2 12.6 13.3 14.6 15.4 16.1 17.6 18.5 19.1
Fresh
Canneil
36.7 38.0 38.2 38.9 39.2 39.2 39.2 39.5 40.2 40.9
25.3 26.7 27.1 27.6 28.4 29.5 29.6 30.3 29.8 29.4
'Raw flesh color measured by the Hunter al. reading prior to canning was used as maturity index. The disappearance of greenish color and increasing maturity was indicated by a higher al. value. 'The "fresh" values refer to readings taken on individual raw peach halves while those of the "canned" to whole cans. 'Color index used by Dei-Tutu et al. (1970) I Hue was calculated as tan" a,/bl.' The hue angle increases as it changes from pale-green to orange-yellow. "'Saturation was calculated as (at.' + bt.'),n. It is proportional to the strength of color.
Maturity and yield Previous work at the Horticultural Research Institute of Ontario (Upshall, 1943) demonstrated that premature freestone peaches were smaller than mature ones. To investigate the relationship between maturity and fruit size, the average drained weight of the canned halves for each maturity group was recorded (Table 5). The peaches in the 2 to 4 maturity group had almost reached their full size. Howeve.r, less mature peaches were considerably smaller. Haryestmg before that stage of maturity would result in slgmficantly lower yield for the grower.
Conclusions The results showed that flesh color is a good index of for Ontario-grown clingstone peaches. The flesh ~olor of raw peaches could be reliably measured by Hunter ~ values USll~g a Hunterlab Color and Color Difference th:ter. Matunty affected the color, flavor and texture, in th ~t order, of the canned peach halves. Canning improved ~ ~olor, particularly with fruit not fully mature. The best ljua tty canned products were obtained from fruit with ~atunty
45
Table 5. Drained weight of canned peach halves processed at different maturities within 24 hours of harvest. _B_a_b.:...y:::.go_l_d_5
Below -2 -2 toO Ot02 2 t04 4t06 6 t08 8 to 10
-...:B:....:a-...:b.:'..yE.go:....:l_d_7_~ I
Maturity group I
i
Avg wt per half, g , 49.3 56.0 51.6 66.4 68.9 64.0 78.9
54.4 60.1 63.9 71.0 71.5 76.7 73.4
, Raw flesh color measured by the Hunter al. reading was used as malUrity index. The disappearance of greenish color and increasing malUrtlY' is indicated by higher at. value. Larger sides of the peaches were canned.
Hunter a L readings of 4.0 to 6.0 in the case of Babygold 5 and 10.0 to 12.0 in the case of Babygold 7. Picking imma' ture fruits would reduce the yield as well as lower the qual' ity of the canned product. J. Insl. Can. Sci. Technol. Aliment Vol. 8. No.4. 191'
l.4ckDowledgements The authors are indebted to Dr. G. C. Ashton, Dr. I. McMillan and Mrs. Jeanette Hines, University of Guelph, Guelph for statistical advice and computer analysis of the data. W. R. Breckenridge, J. F. Mott, N. G. Pearson and VI Routby, Canada Department of Agriculture, Fruit and v~getable Inspection Service; .0. qement and H.. Holt, eanadian Canners Ltd., HamIlton; B. Roberts, NIagara Food Products Ltd., Stoney Creek, for their expert grading of the canned peaches; J. C. Rider, Canadian Canners Ltd., St. Catharines and O. A. Bradt for advice and supplying the peaches; Judith L. Allison, R. B. Palabay and other members of the Hor~icultural Pro.ducts ~aboratory staff of this Institute for theIr able techmcal assIstance.
..
Can.)nsl, Food Sci. Technol. J. Vol. 9, No. I, 1976
References Anon. 1966. Cling peach maturity study using Agtron instrument. Calif. Dept. Age.• Mimeo. 7 p. Claypool. L. L. 1966. Maturity indices for processing clings and freestones. In, Summary of the National Peach Conference. New Brunswick. N.J., March I J -12, 1965. 179. Dei-Tutu. J .. Edwards. R. A. and Buckle, K. A. 1970. Pigments and colour of Australian peach varieties. Food Techno!. Australia 22: 272. Fuleki. T. 1971. Methods for tristimulus colorimetry of apple. clingstone peach. tart cherry. tomaw juice and wine. HOft Res. Inst. of Ont Rep. for 1970: 137. Kerlinger, F. N. 1973. Foundations of Behaviourial Research. Holt, Rinehart and Winston, New York. Leonard, S. J.. Luh, B. S. and Hinreiner. E. 1953. Flavor evaluation of canned cling peaches. Food TechnoJ. 7:480. Leonard, S. J.. Luh, B. S.. Chichester. C. O. and Simone. M. 1961. Relationship of fresh clingstone peach color to color and grade after canning. Food Techno!. 15:492. Steel. R. G. D. and Torrie. J. H. 1960. Principles and Procedures of Statistics. McGraw-Hili, New York. Upshall. W. H. 1943. Increase in quantity. grade and returns from peaches as they approach opti· mum maturity. Sci. Agr. 23: 747.
Received June 27. 1975
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