The Effects of Harvest Date on Thompson Seedless Grapes and Raisins. II. Relationships of Fruit Quality Factors

Transcription

1 The Effects f Harvest Date n Thpsn Seedless Grapes and Raisins. II. Relatinships f Fruit Quality Factrs L. PETER CHRISTENSEN 1 *, MARY L. BIANCHI 2, MARTIN W. MILLER 3, AMAND N. KASIMATIS 4, and CURTIS D. LYNN s The fresh fruit and raisin cpsitin and quality factrs easured during a three-year Thpsn Seedless raisin harvest study were cpared by regressin analysis t deterine their relatinships and suitability as predictrs f raisin quality. Raisin quality was easured with the airstrea srter as percent B and better (%B&B) and percent Substandard (%Sstnd) raisin grades. The relatinship f fresh fruit sluble slids (SS) t the drying rati f raisins was als analyzed. The ain fruit easureents analyzed as a predictr f raisin quality were fresh fruit SS and titratable acidity (TA) and raisin reducing sugars (RS) and TA. Sluble slids and drying rati shwed a highly significant linear relatinship, with a cefficient f deterinatin (R 2) f , but with a different calculated prduct f their values as cpared t earlier reprts. Fresh fruit SS and TA were curvilinear and linear, respectively, t %B&B raisin grade. The relatinship f fresh fruit TA t %B&B raisin grade is explained by TA's curvilinear relatinship t SS rather than a direct effect f TA n raisin quality. The regressin cparisn f the RS and TA cntent f raisins shwed a high cefficient f deterinatin (R 2 = ) and bth shwed a highly significant linear relatinship t %B&B and %Sstnd raisin grades. Many f the paraeters shwed relatinships siilar t thse fund in earlier studies, including the fresh fruit SS and raisin TA crrelatin t raisin quality; se differences indicate need fr further study under re current raisin grape grwing cnditins. KEY WRDS: Vitis, grapes, raisins, Thpsn Seedless, cpsitin, quality The fresh and dried fruit factrs which influence raisin yield and quality are iprtant t the harvesting, prcessing, and arketing decisins f raisin grwers and packers. Sluble slids (sugar) cntent is knwn t greatly affect the rati f fresh t dry fruit (4,5) and the subsequent raisin yield and quality (4,5,6,7). This is largely due t the high prprtin f grape sugar which cntributes t raisin cpsitin. Jacb (4) reprted 80.% t 84.4% reducing sugars (RS) n a dry weight basis fr raisins fr Thpsn Seedless grapes ranging fr 18.0 t 29.0 Balling; the authrs in a previus reprt (3) reprted 76.3% t 84.0% RS in raisins fr grapes f 15.2 t 21.0 Brix. Jacb (4,5) als studied the relatinships f varius factrs f fruit cpsitin and raisin quality. He fund sluble slids (SS) f the grapes, titratable acidity (TA) f raisins, and weight per unit vlue f raisins t be clsely related t visual grades f raisin quality. Mre recently, Kasiatis (7) shwed highly significant relatinships f grape SS and berry weight t airstrea srter raisin grades, an bjective ethd adpted by the Califrnia industry during the 1960s (1,7). Kasiatis' wrk cntrasted with that f Jacb's in that the fruit was characteristic f vineyards in the 1Extensin Viticulturist, Departent f Viticulture and Enlgy, Univ. f Califrnia, Davis and Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier, CA 93648; 2Far Advisr, University f Califrnia Cperative Extensin, 2156 Sierra Way, Suite C, San Luis bisp, CA 93401; 3Prfessr Eeritus, Departent f Fd Science and Technlgy, University f Califrnia, Davis, CA 95616; 4Extensin Viticulturist Eeritus, Departent f Viticulture and Enlgy, University f Califrnia, Davis, CA 95616; scunty Directr Eeritus, University f Califrnia Cperative Extensin, Visalia, CA *Crrespnding authr. Manuscript subitted fr publicatin 29 Nveber Cpyright 1995 by the Aerican Sciety fr Enlgy and Viticulture. All rights reserved. present-day raisin prductin districts and f larger berry sizes and at a lwer range f grape aturity than that f Jacb. Jacb's raisin evaluatins indicated a linear relatinship f raisin quality t grape SS while Kasiatis shwed a highly significant curvilinear regressin line. These differences ight be explained by the differences in fruit characteristics due t widely different grwing areas and cnditins as well as the ethd f evaluating quality. Certainly, the differences pint t the need t reevaluate raisin cpsitin and quality factrs under grwing cnditins and with fruit which are characteristic f tday's raisin industry. Cparisn with the airstrea srter is als needed t ake the infratin relevant t present industry quality grading standards. Althugh the present study was cnducted in the 1960s, the ethds f analysis and the grwing cnditins are relevant t current industry standards. The data input fr the previus paper (3) and present statistical analysis capabilities prpted the culinatin f this wrk as presented. Materials and Methds The study was cnducted in a typical, cercial Thpsn Seedless raisin vineyard suth f Fresn, Califrnia, ver three years, 1964 t Fruit was harvested ver five weekly harvest dates in 1964 and 1965 and three dates in 1966 fr plts in a Latin square trial design. Fresh berry saples were analyzed fr SS as Brix, TA, berry weight, and berry vlue. Harvest weights were taken befre and after raisin drying fr yield and drying rati deterinatins. Raisin saples were taken fr percent isture 493

2 CHRISTENSEN et al deterinatin, RS analysis, TA deterinatin, and airstrea srter grades fr percent B and better (%B&B) and percent substandard (%Sstnd). The airstrea srter grades were based n settings f and inch (1.359 and 0.80 c) f air pressure differential. Further details f trial design and ethds f analysis are presented in the previus paper fr the sae study (3). The previus paper als explains hw current industry airstrea srter settings cpare with thse used in this study. Regressin analyses were cnducted n the treatent eans f the fresh fruit and raisin easureents t deterine their relatinships and hw they ay serve as a predictr f raisin quality. The ain cparisns were fresh fruit SS as Brix, fresh fruit TA, raisin TA, and raisin RS. Results The regressin equatins, cefficients f deterinatin (R2), and levels f significance fr the cparisns are given in Table 1; the graphs fr the regressin cparisns which were statistically significant (p = 0.05) are presented in Figures 1 thrugh 9. Each ain cparisn includes the airstrea srter grades f %B&B and %Sstnd as a predictr f raisin quality. Fresh fruit sluble slids ( Brix): Seven cparisns were ade with SS as listed in Table 1. Sluble slids in Figure 1 shwed a highly significant linear relatinship t the drying rati f fresh grapes t raisins (R 2 = ). Sluble slids and TA f fresh grapes in Figure 2 shwed a highly significant curvilinear relatinship (R 2 = ). Sluble slids and %B&B raisin grade in Figure 3 als shwed a significant curvilinear relatinship (R 2 = ). The cparisns with raisin RS, raisin TA, %Sstnd raisin grade, berry weight, and berry vlue were nt significant (Table 1). Fresh fruit titratable acidity: Titratable acidity (expressed as gras tartaric/100 L) in Figure 4 shwed a significant linear relatinship t %B&B raisin grade and with a R 2 f The cparisns with raisin TA and %Sstnd raisin grade were nt significant (Table 1). Raisin titratable acidity: Raisin TA in Figures 5 and 6 shwed a highly significant linear relatinship t bth raisin grades, %B&B and %Sstnd. Raisin reducing sugars: Reducing sugars in raisins shwed a highly significant linear relatinship t raisin TA in Figure 7 and t bth raisin grades, %B&B and %Sstnd in Figures 8 and 9. Discussin The highly significant linear relatinship f SS t raisin drying rati with a R 2 f is in agreeent with the earlier wrk f Jacb (4). Jacb reprted a crrelatin cefficient f fr Thpsn Seedless fruit sluble slids and drying rati f natural, sundried raisins and cncluded that the relatinship apprxiated a straight line functin. His calculated Table 1. Regressin analysis f fresh grape and raisin cpsitin and quality paraeters, Thpsn Seedless date f harvest study, Regressin equatins represent regressin n plt eans fr each date f harvest. Equatin R 2 P> Sluble slids ( Brix) f fresh fruit as a predictr Drying rati f fresh t dry fruit: Y = X Titratable acidity f fresh fruit: Y = X X Y = X X 2 Reducing sugar in raisins: Y = X Titratable acidity f raisins: Y = X Airstrea srter Substandard grade: Y= X Berry weight: Y = X Berry vlue: Y = X Titratable acidity f fresh fruit as a predictr Y = X Titratable acidity f raisins: Y = X Airstrea srter Substandard grade: Y = X Titratable acidity f raisins as a predictr Y = X Airstrea srter substandard grade: Reducing sugar f raisins as a predictr Airstrea srter Substandard grade: Y = X Y = X Titratable acidity f raisins: Y = X prduct f SS ( Bailing) and drying rati fr natural sun-dried raisins averaged 87.8 (5) and varied little ver the entire range f SS. In cparisn, the calculated prduct f SS ( Brix) and drying rati in this study averaged While the reasn fr the difference in these values between the studies is nt knwn, the present Fresn study represented a lwer range f fruit aturity and larger berries than was used in the Jacb study. Als, Jacb cnducted his study under different sil, cultural, and gegraphical cnditins. These differences pint t the need t further deterine drying ratis under re current cnditins but with a wider range f fruit aturity than encuntered in this study. The ther significant relatinships with SS -- fresh fruit TA and %B&B raisin grades -- were curvilinear as has been previusly reprted (2,8,9). Bth are

3 -. THMPSN SEEDLESS GRAPES AND RAISINS. II "I I 5.4 R ~ = *** ~ =5.3...,,... ~... ~... ~-~...'5.1 == ~, ~~ - 4.9,- 0.c 4.8 [] = " 4.7 ~ a 4.6 = 4.5 _ 4.4 "~ 4.3 1: & Sluble slids ( Brix) Fig. 1. Regressin f plt eans fr fresh fruit sluble slids ( Brix) and drying rati f fresh fruit t raisins, 1964 thrugh *** Significant at p = ==1 " - ~.7 >, _.e 0.6".~ i- 0.5" 0.4,= ~~n 0 0 I 0"~ [] <> 1965 z~ 1966,,,,,,,,, i,,,,~ ~,,,1,,,~,~ r,, [,,,,,, ~,, I~ ~,-,,,, 1,,-,,,~,',,' Sluble slids ( Brix) Fig. 2. Regressin f plt eans fr fresh fruit sluble slids ( Brix) and titratable acidity, 1964 thrugh *** Significant at p = R 2= ~i 10 R = ~. ~ 80 -~ 70 " e,, i 60" ~ 50 -,,~,.,,,I,,,N~,HI,,,,~,~,~I~,,,,~,I~,,,,,,,, I,,~,~,,~, Sluble slids ( Brix) / ~ & ~z~ 7 <>!90S i /. z~ 1966 ii,/ -, ~i Fig. 3. Regressin f plt eans fr fresh fruit sluble slids ( Brix) and airstrea srter % B and better raisin grade, 1964 thrugh * Significant at p = well recgnized fr their clse relatinship t SS. Hwever, raisin RS did nt shw a significant relatinship t SS. Jacb (4) fund that raisin RS shwed a general but sall increase with increasing SS up t abut 23 t 24 Brix and with a crrelatin cefficient f He attributed the pr relatinship f SS and raisin RS t the sall range and the inherent variability fund in the cheical deterinatin f raisin RS which was 80 J~ ~ 70 90,, <> 1965 [] ~,,~ z~1966 : : --,, Titratable acidity (8/100 L) Fig. 4. Regressin f plt eans fr fresh fruit titratable acidity and airstrea srter % B and better raisin grade, 1964 thrugh * Significant at p = re r less epirical (5). Fresh fruit TA shwed a significant linear relatinship t %B&B raisin grade. This ay be attributed t the clse relatinship f TA t SS in fresh fruit (Fig. 2) rather than a direct influence f TA n raisin quality. Sluble slids cntent wuld be expected t be a better predictr f raisin quality as indicated by the higher cefficient f deterinatin fr %B&B raisin grade in

4 CHRISTENSEN et al " (g 01 8 I_.Q " " 70 t~ <> I:3 n Acid raisins (%) Fig. 5. Regressin f plt eans fr raisin titratable acidity and airstrea srter % B and better raisin grade, 1964 thrugh *** Significant at p = " " " %. " 5 E " W,', 4 =1 t~ 3 2 f 1965 zx ~ ~ 0 [] 0 > ~ 0 0 [] ~ Zk ' "'"''"['""''"i'"... "1"""~"1 ''''''''' Acid raisins (%) Fig. 6. Regressin f plt eans fr raisin titratable acidity and airstrea srter % substandard raisin grade, 1964 thrugh ** Significant at p = ~ 2.25 ~, ~,, [3 _ \ " ~ "~ 4~. d>[] A 4~A~ ~ -, I... I... I... I... I... I iiii1...,11,11,,11... llllrillll I Reducing sugars (%) Fig. 7. Regressin f plt eans fr raisin reducing sugars and raisin titratable acidity, 1964 thrugh ** Significant at p= this study as well as its direct and well established effect n airstrea srter grades (2,6,7). The pr relatinship f fresh fruit TA with raisin TA ight see surprising, except that Jacb (5) als reprts siilar findings within the sae range f fruit aturity as in this study. Jacb fund that the fresh fruit TA was higher than raisin TA at aturities up t 23 Brix when cnsidering the factr f water lss by calculatin fr the drying rati. We reprted siilar A ~ 90-8!_ 1 %.. 70 " e- Ca z~ A 0 n cp [] ~ zx Reducing sugars (%) Fig. 8. Regressin f plt eans fr raisin reducing sugars and airstrea srter % B and better raisin grade, 1964 thrugh ** Significant at p =0.01. results in the previus paper (3). Jacb suggested that this difference ay be due t acid lss fr respiratin during the drying prcess. The highly significant linear relatinship f raisin TA t raisin quality is in agreeent with Jacb (4,5). Jacb suggested that raisin TA shuld be cnsidered as a pssible indicatr f raisin quality with grapes between 18 and 23 Brix. His data shwed a rapid decrease in raisin TA as grape aturity advanced within this aturity range. Hw-

5 THMPSN SEEDLESS GRAPES AND RAISINS. II v - 7 "a e. 5.Q. ~ 4 U) 0 ~ A A % : N, "~..,.= R 2 = *** 1965 z~ ,,,,i,,,,i,,,,l,,,, l,,,,l,,,,[r,,,l,,,,l,,,,l,,,,l,,,vlv.,l,,,,i,,,,l,.,, Reducing sugars (%) Fig. 9. Regressins f plt eans fr raisin reducing sugars and airstrea srter % Substandard raisin grade, 1964 thrugh *** Significant at p= ever, this decrease in raisin TA nearly ceased as the fruit becae very ripe. Jacb's explanatin fr the better relatinship f raisin TA t grape aturity and quality (as cpared t fresh fruit TA) was the pssibility t include disslved ptassiu bitartrate in the deterinatin. As grapes ripen, the prprtin f ptassiu bitartrate relative t free acid increases. This ptassiu bitartrate wuld nt be included in the fresh fruit TA analysis but the free tartaric wuld be included. Hwever, with the raisins, ptassiu bitartrate wuld be disslved and leached with the ht water extractin ethd and thus be represented in the acid cntent f the raisins. Certainly, the specific reasn fr the relatinship f raisin TA t raisin quality cannt be deterined fr this study. Hwever, the agreeent between the tw studies further suggests raisin TA as a ptential index f raisin quality. The reasn why raisin RS shwed a highly significant relatinship with airstrea srter raisin grades as cpared t fresh fruit SS cannt be explained. Jacb (4,5) iniized the value f raisin RS because f the relatively sall changes during ripening and the variability and epirical nature f the analytical ethd. Als, at the aturity range abve 24 Brix there were n appreciable changes in raisin RS in Jacb's study. Hwever, the present study invlved a narrwer range f fruit aturity and pssibly a re precise analytical ethd which ay accunt fr the better relatinship f raisin RS t raisin quality as cpared t Jacb. Als, it is pssible that se f the variables such as berry sapling ethd r the influence f berry weight was eliinated with the raisin RS ethd as cpared t fresh fruit SS. Cnclusins This wrk cpares by regressin analysis the characteristics and cpsitin f fresh grapes and raisins fr the three-year Thpsn Seedless raisin harvest study. When apprpriate, cparisns are ade with the earlier study f Jacb's (4,5). It shws the highly significant linear relatinship f fresh fruit SS t raisin drying rati. Hwever, differences in the prduct f SS and drying rati between this study and Jacb's earlier wrk pints t the need t further develp drying rati infratin using re current cnditins f raisin prductin. Fur ain cparisns f fruit easureents as a predictr f raisin quality were used: SS and TA f fresh fruit and RS and TA f raisins. Sluble slids shwed a significant curvilinear relatinship t %B&B raisin grade as has been shwn in previus studies (2,7). This is explained by the predinant influence f grape sugar n the quality f raisins (4,5). Fresh fruit TA shwed a significant linear relatinship t %B&B raisin grade. This relatinship is explained by the highly significant curvilinear relatinship between fresh fruit SS and TA. Thus, fresh fruit TA's relatinship t raisin quality wuld be expected t be indirect and due t its clse relatinship t SS. The RS and TA cntent f raisins were highly crrelated t ne anther and bth shw a highly significant linear relatinship t %B&B and %Sstnd raisin grades. The clse relatinship between raisin TA and raisin quality agrees with Jacb's findings; hwever, raisin RS had nt been previusly shwn t accurately predict raisin quality, pssibly due t less accurate analytical ethds in earlier years. verall, any f the fruit relatinships fund in this study were siilar t thse f Jacb's. Differences reprted here ay be largely due t the widely different gegraphical and vineyard cnditins between the studies and the resulting saller berries and uch higher range f fruit aturities in Jacb's study. This ay explain the differences in drying ratis and indicates the need fr further study. Literature Cited 1. Annyus. Instructins fr inspectin and certificatin f natural cnditin raisins. USDA Cnsuer and Marketing Serv. Fruit and Vegetable Div. Prcessed Prducts Standardizatin Branch. (1964). 2. Baranek, P., W. M. Miller, A. N. Kasiatis, and C. D. Lynn. Influence f sluble slids in Thpsn Seedless grapes n airstrea grading fr raisin quality. A. J. Enl. Vitic. 21: (1970). 3. Christensen, L. P., M. L. Bianchi, C. D. Lynn, A. N. Kasiatis, and M. W. Miller. The effects f harvest date n Thpsn Seedless grapes and raisins. I. Fruit cpsitin, characteristics, and yield. A. J. Enl. Vitic. 46:11-16(1995). 4. Jacb, H. E. The relatin f aturity f the grapes t the yield, cpsitin, and quality f raisins. Hilgardia 14: (1942). 5. Jacb, H. E. Factrs influencing the yield, cpsitin, and quality f raisins. Calif. Agric. Expt. Sta. Bull (1944). 6. Kasiatis, A. N., E. P. Vilas, F. H. Swansn, and P. P. Baranek. A study f the variability f Thpsn Seedless berries fr sluble slids and weight. A. J. Enl. Vitic. 26: (1975).

6 498 CHRISTENSEN et al 7. Kasiatis, A. N., E. P. Vilas, F. H. Swansn, and P. P. Baranek. Relatinship f sluble slids and berry weight t airstrea grades f natural Thpsn Seedless raisins. A. J. Enl. Vitic. 28:8-15. (1977). 8. Radler, F. The effect f teperature n the ripening f Sultana grapes. A. J. Enl. Vitic. 16:38-41 (1965). 9. Winkler, A. J., J. A. Ck, W. M. Kliewer, and L. L. Lider. General Viticulture (2 n'j Ed.). University f Califrnia Press, Berkeley (1974).