zyxw zyxw zyxw INFLUENCE OF YEAR, CULTIVAR AND FRUIT MATURITY ON QUALITY OF PEACH PUREE' A.R. GONZALEZ, A. MAUROMOUSTAKOS and G. PROKAKIS zyxwv zyxw Department of Food Science University of Arkansas J. ASELAGE Gerber Products, h c . , P.0.Box 10010 Ft. Smith, Arkansas Received for Publication November 25, 1991 ABSTRACT A 3-year study was conducted to evaluate the effect of year, cultivar and fruit maturity on the quality ofpeach puree and to determine the relative importance (RJ of these factors on the quality components hue angle (color), pH, acidity, soluble solids (SS and SYacid ratio. The results indicated that year, cultivar cnzdpuit maturity had a strong effect and that they are very important in determining the quality of peach puree by affecting the different quality components. h general, JLuit maturity had stronger RI than year and cultivar on the quality parameters studied. l'he data obtained f i r different maturities and cultivars jit a linear regression that accounted for 95% of the variability f i r all quality parameters measured. p H and SYacid ratio increased nhile acidity and hue angle decreased and SS showed small or no increase as the fruit reached more advance stages of maturity. zyxw zyxw INTRODUCTION One of the main goals of a peach processor is to pack a high-quality product throughout the packing season year after year. Early-, mid- and late-season peach zyxw zyxwvut 'Approved for publication by the Director of the Arkansas Agricultural Experiment Station. Journal of Food Quality 15 (1992) 97-109. All fights Reserved. 0 Copyright 1992 by Food & Nutrition Press, h c . , Trumbull, Connecticut. 97 98 zyxwvutsrq zyxw zyx A.R. GONZALEZ,A. MAUROMOUSTAKOS and G . PROKAKIS zyxw zyxwvu zy cultivars contribute to a continuous flow of raw product in the processing plants. These cultivars, which are well adapted to the growing area and have desirable field and fruit quality attributes, play an important role in the quality of the raw and processed product (Sistrunk 1985). However, cultivar practices (irrigation, pruning, fruit thinning, fertilization, diseases and pest control) and favorable environmental conditions (rain, sunlight, temperature and humidity) from planting to production stages may also contribute to the quality of the raw and processed product (Claypool et d.1971; Kader et d.1982; Sistrunk 1985; Sweeney et d. 1970). Even though cultural practices can be efficiently manipulated, the environmental factors may influence the final outcome of the raw product quality. Researchers working with fresh-market (Rood 1957; Sistrunk 1985; Shewfelt d d.1987; Meredith d d.1989; Peterson d d.1989; and Robertson d d.1990) and processing peaches (Kader ef d. 1982 and Sistrunk 1985) agree that fruit maturity is the most important single factor affecting the quality of peach fruits. Since fruits do not ripen uniformly on the trees, a high percentage of immature fruits is present in mechanically or manually harvested peaches, and they may affect significantly the quality of processed product. Attempts have been made to increase the amount of ripe fruits on the tree before harvest by using Daminozide (Morris d d.1978 and Sims 1988), and Ethephon (Sims et d.1974) with partial success. Postharvest treatments with ethephon have also helped to accelerate ripening of peaches (Dekazos 1985), but from the processor’s point of view, postharvest treatments create problems of space and storage time. Quality is comprised of the composite effect of a series of quality components. Some of these components are more important than others and can be affected by factors such as climatic conditions, cultural practices, cultivar and fruit maturity. Some of these factors can be manipulated in a commercial operation; however, climatic conditions cannot. From the processors point of view, there is interest in knowing the relative importance of these factors on the quality components. The information generated in this research may contribute to improvement in the quality of processed peaches. The objectives of this research were to determine the relative importance of year, cultivar and fruit maturity on quality of peach puree and to evaluate the effect of these three factors on hue angle, pH, titratable acidity, soluble solids and soluble soliddacid ratio. MATERIALS AND METHODS This study was conducted during the 1988, 1989 and 1990 growing seasons from peaches grown in the area of Forrest City, Arkansas. The fruits utilized in the study were obtained from the same commercial orchard. Three clingstone zyxw zy zyxwv zyxwv zyx QUALITY OF PEACH PUREE 99 peach cultivars were included in the study: Allgold, an early-season cultivar developed in Arkansas (Moore et al. 1984), Baby Gold 5 and Baby Gold 7, midand late-season cultivars developed in New Jersey (Brooks and Olmo 1972). Seven maturity stages were included in the study. Peaches were separated by using the ground color chips developed for freestone peaches by Delwiche and Baumgardner (1985) in which chip 1 corresponds to mature green and chip 6 to full ripe. Maturity 7, corresponding to overripe, was added to our study. Chips 2 to 5 corresponded to a gradual increase of intermediate maturities. One bushel of peaches for each of the seven maturities in each cultivar was sorted in the orchard and later used to make the puree. The bushel content was divided in three parts; each part corresponded to a replication. The fruits were peeled in a 8.5% lye solution heated to a boiling point, rinsed with tap water, mechanically pitted and sliced, steam blanched for 4 min and then pulped in a finisher with a 0.6858-mm mesh. Ascorbic acid at a concentration of .06%was added to the puree to reduce color changes due to oxidation. The puree was poured into an 8-oz 2 1 1 x 304 plain tin cans. The cans with puree were exhausted in live steam for 4 min, sealed and processed in boiling water for 25 min. The cans were stored at 4C until analysis. The quality parameters evaluated in peach puree were color measured by hue angle, pH, acidity, SS and SS/acid ratio. These quality parameters have consistently been used by researchers working with fresh-market and processing peaches (Kader et al. 1982; Shewfelt et al. 1987; and Meredith el al. 1989). Acidity and pH were measured on a 10 g puree samples diluted in 50 mL of deionized water. pH was measured with an Orion pH meter, model 407, that was standardized with a pH 4.0 and 7.0 buffer solutions. The sample was titrated to pH 8.3 with a 0.1 N NaOH solution and reported as a percentage of citric acid. Soluble solids were determined by filtering a puree sample at room temperature (20C) through a Kim-wipe tissue in a Bausch and Lomb Abbe refractometer. Color was determined with a Gardner Color Difference Meter (Colorguard System 1000 colorimeter, GardnedNeotec Instrument Division - Pacific Scientific Co., Silver Spring, Maryland) that was standardized with a white plaque (L = 94.47, a = -0.81, b = -0.86). Hue angle (tan- ‘b/a) was calculated as indicated by Little 1975. The SS/acid ratio was calculated with the SS and the acidity data corresponding to each sample. The fixed effects of year, cultivar and maturity were evaluated in an analysis of variance. The year effect was tested with the replications nested in years. The main effects of maturity and cultivar, all the two-way interactions of the three factors and the three-way interaction were tested with the residual mean square error. Our measure of the relative importance (RI) of a factor is based on the approach of McNew (1985). If one were to “predict” the true mean for a combina- zyxw zyxw zyxwvutsr 100 zyxwvutsrq zyxw zyx A.R. GONZALEZ, A. MAUROMOUSTAKOS and G . PROKAKIS zyxw tion of factors by using all effects except the main effects of one factor, then the magnitude of the “prediction error” would reflect the importance of that factor. That is, the larger the magnitude of the error, the more important is that factor. The mean square of these errors across all factor combinations represents the average importance of that factor. The RI of one factor to another is defined as the ratio of their mean-squared errors. These mean-squared errors are estimated from the data by subtracting the experimental variability from the observed mean squares in the analysis of variance. In Table 1, “1X” designates the smallest mean-squared error estimate for a quality parameter among year, cultivar and maturity. The entries for the other two factors describe their RI in reference to this factor. To identify trends, the maturity source of variation was partitioned into the linear regression of maturity and in the higher order components of nonlinearity. The cultivar x maturity, year X maturity, and year x cultivar x maturity were partitioned in a corresponding manner. RESULTS AND DISCUSSION In our study, in which the effects of year, cultivar and fruit maturity were incorporated, it was observed that year had a very strong impact relative to maturity and cultivar on S S (sugars), strong on hue angle and acidity and minimum on pH and SS/acid ratio (Table 1). Cultivar, on the other hand, had a strong impact on pH and SS, an intermediate effect on Wacid ratio and a minimum influence on acidity and color (Table 1). Fruit maturity had a relatively strong impact on SS/acidity ratio, pH and acidity; an intermediate effect on hue angle; and a minimum impact on SS (Table 1). From the practical point of view, growing conditions are difficult to control; however, cultivar selection and harvesting of more advanced h i t maturities would help to capture the best quality of raw product, hence the processed product, in any specific growing condition. Trend analysis based on maturity showed that the linear component accounted for approximately 95 % of the variability for all quality parameters studied. The linear regressions for each quality parameter on maturity were significantly different at the 5 % significance level among the variety-year combinations. The nonlinearity components (quadratic and cubic) were not significant at the 5 % significance level. The analysis showed a decrease in hue angle values from maturity 1 to maturity 7; this trend was observed in all cultivars during the 3-year study (Fig. 1). Rood (1957), Kader et al. (1982), Sistrunk (1985), Meredith et d.(1989) and Robertson et al. (1990) have reported an increase in orange color (CDM ‘a’) from immature to mature fruits. Cultivar differences in hue angle were observed zyxw zyxw zyxwv zy 101 QUALITY OF PEACH PUREE z TABLE 1 RELATIVE IMPORTANCE OF YEAR, CULTIVAR AND FRUIT MATURITY ON THE QUALITY OF PEACH PUREE Variable Year Hue Angle PH Acidity (A) Soluble solids (SS) SS/A Ratio FactorY Cult ivar Maturitv I zyxwv 3xz 1x 2x 1x 9x 7x 2x 1x 3x 60X 2 ox 1x 1x 3x 9x zyxw zyxwv zyxwv zyxwvutsr The higher the coefficient of X, the more important the factc for that particular quality parameter. ' Based on the mean-squared prediction error when that particul factor was omitted from the analysis. between Allgold, Baby Gold 5 and Baby Gold 7. Differences between cultivars were reported by Kader et al. (1982) and Sistrunk (1985). The latter reported that early-maturing cultivars have lighter color than late-maturing cultivars. In our study, the early-season cultivar Allgold had better or similar hue angle than Baby Gold 5 and Baby Gold 7, which are a mid- and late-season cultivars, respectively. Differences in hue angle values were inconsistent from year to year, indicating that there was a significant year % cultivar interaction (Fig. 1). Quantitative differences in color due to yearly growing conditions have been reported by Kader et al. (1982). With the exception of Baby Gold 5 in 1989, pH increased as the fruit reached more advanced stages of maturity (Fig. 2). Similar trends were observed by Deshpande and Salunkhe (1964), Kader et al. (1982) and Sistrunk (1985). Differences in pH were noted between cultivars; however, the early cultivar Allgold had the highest pH at maturity 7 in the years studied. Differences in pH between cultivars and years have been reported by Sweeney et al. (1970) and Kader et zyxwv d. (1982). In contrast to pH values, the acidity of peach puree decreased as the fruits reached maturity 7 (fig. 3). A similar trend was reported by Allen (1932), Rood (1957), Kader et al. (1982), Sistrunk (1985), Meredith et d.(1989) and Robertson et ul. (1990). Distinct differences in acidity were noted between cultivars; however, in the three years studied the cultivar Baby Gold 5 consistently had the highest values (Fig. 3). Cultivar differences in acidity were reported by Allen 0 0 zyxw zyxwvu --------- -i--------- zyxwvutsrqp zyxwvutsr 1 I I 2 3 zyxw 1 4 I I I 1 8 'I S T A G E OF MATURITY FIG. 1. REGRESSION OF HUE ANGLE OF THREE CULTIVARS ON STAGE OF MATURITY The regression for each year studied is presented separately. QUALITY OF PEACH PUREE 103 1 I 4 5 zy YEAR=19E9 3 s 3.m 386 3.80 3.75 1 2 3 S T A G E OF MATURITY zyx 6 FIG. 2. REGRESSION OF pH OF THREE CULTIVARS ON STAGE OF MATURITY The regression for each year studied is presented separately. 7 zyxwvu zyxwvu YEAR-1988 om om FIG.3. REGRESSION OF ACIDITY (96 CITRIC ACID) OF THREE CULTIVARS ON STAGE OF MATURITY The regression for each year studied is presented separately. zy zyxwvu zyxwvu zyxw zyxwvu QUALITY OF PEACH PUREE 105 (1932), Sweeney e? d.(1970), Kader et al. (1982) and Sistrunk (1985). Sistrunk (1985) reported that early season cultivars have a high level of acidity; however, this relationship was not apparent in our study. The impact of year on acidity indicated that growing conditions affected acidity of peaches. Sweeney et d.(1970) and Kader e? d.(1982) found similar results. Contrary to reports indicating an increase in SS or sugars as peach fruits reach advanced stages of maturity (Allen 1932; Rood 1957; Deshpande and Salunkhe 1964; Kader er al. 1982; Sistrunk 1985; Moriguchi et d. 1990; and Robertson et d. 1990), the results of this study showed small or no changes in SS from maturity 1 to 7, indicating that maturity in the cultivars studied had a small impact on the levels of SS (Fig. 4). However, it was apparent from Fig. 4 and Table 1 that cultivar and the year’s growing conditions had a much stronger effect on the levels of SS. Allgold, an early cultivar, had the lowest SS in 1988 and 1990 while Baby Gold 7, a late cultivar, had the highest values in all maturities in 1989 and 1990, and in maturities 1,2, 3 and 4 in 1988 (Fig. 4). These results are in agreement with reports of Allen (1932), Sweeney er d. (1970), Kader e? d.(1982) and Sistrunk (1985) that indicate that late-maturing cultivars have higher levels of SS than early-maturing cultivars. The results indicate that the year-to-year growing conditions and cultivar differences had a stronger impact on the levels of SS than on maturity, as indicated by the fact that most of the lines in Fig. 4 have slopes nearly equal to zero (Table 1, Fig. 4). Sweeney er d.(1970) reported that these changes are mainly due to amount of rainfall and sunshine. Moriguchi et al. (1990) also reported year-to-year changes on total sugars; however, they found that the proportion of sugars did not change. Soluble soliddacid ratio, a parameter frequently used to measure quality of peaches, increased from maturity 1 to 7 (Fig. 5), a trend observed by Deshpande and Salunkhe (1964), Kader et d.(1982), Meredith et al. (1989) and Robertson (1990). In this study, fruit maturity had the highest impact on SS/acid ratio (Table 1). Baby Gold 7, characterized by a high SS content, had the highest SS/acid ratio in all years studied. Baby Gold 5, which had the highest acidity, showed the lowest SS/acid ratio. Allgold had an intermediate ratio (Fig. 5). Differences in SS/acid ratio between cultivars have been reported by Kader et al. (1982) and Sistrunk (1985); however, these differences were not associated with earliness of the cultivars. In our study, Baby Gold 7, a late cultivar, showed the highest SS/acid ratio in the 3 years studied. The year effect had the lowest impact on the SS/acid ratio compared to maturity and cultivar (Table 1). In summary, based on the RI of year, cultivar and fruit maturity on the quality of peach puree, it was determined that fruit maturity had the strongest influence on most of the quality characteristics studied. Furthermore, from the practical point of view, the processor should make an effort to utilize peaches at a more zyxw zyxw I 124. zyxwvutsrq na. 11.4. 10.9. z zyxwvuts 74 a4 oa 1 ::izyxwvutsrq 0 10.9 lo.4 0 0 : I , , , , , ao 1 2 3 4 I 6 S T A G E OF MATURITY FIG.4. REGRESSION OF SOLUBLE SOLIDS OF THREE CULTIVARS ON STAGE MATURITY The regression for each year studied is presented separately. I zy a4 YEAR-1988 n 1 2 z zyxwvu zyx HQ m - 5 zyxwvutsrq 3 4 7 S T A G E OF MATURITY FIG. 5 . REGRESSION OF SOLUBLE SOLIDS/ACID RATIO OF THREE CULTIVARS ON STAGE OF MATURITY The regression for each year studied is presented separately. 108 zyx zyxwvutsrq A.R. GONZALEZ, A. MAUROMOUSTAKOS and G. PROKAKIS advanced stage of maturity. Cultivars also had an impact on the quality of peach puree, indicating that the selection of cultivar still plays an important role in the quality of final processed product. Year (growing season), a factor difficult to manipulate, also has an effect on quality of peach puree. ACKNOWLEDGMENT This research was supported in part by a grant from Gerber Products Co. zyxwv REFERENCES ALLEN, F.W. 1932. Physical and chemical changes in the ripening of deciduous fruits. Hilgardia 6(12), 381441. BROOKS, R.M. and OLMO, H.P. 1972. Register oflvew Fruit and Nut Vurien'es. 2nd Ed. p. 333. University of Cal. Press, Berkley. CLAYPOOL, L.L., URIU, K., LEONARD, S. and LASKER, P.F. 1971. The influence of cultural practices on the quality of 'Dixon' cling peaches. Res. Prog. Rpt., Dep. of Pomology, Univ. of Cal., Davis. DEKAZOS, E.D. 1985. Effects of postharvest treatments on ripening and quality of Baby Gold 7 peaches. HortScience 20(2), 240-242. DELWICHE, M.J. and BAUMGARDNER, R.A. 1985. 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