CHEMICAL AND PHYSICAL CHANGES DURING MATURATION OF MUSCADINE GRAPES (VITIS R OTUNDIFOLIA)

CHEMICAL AND PHYSICAL CHANGES DURING MATURATION OF MUSCADINE GRAPES (VITIS R OTUNDIFOLIA) D. E. Carrll and J. E. Marcy Respectively, Assciate Prfessr, Department f Fd Science, Nrth Carlina State University, Raleigh, Nrth Carlina 27650 and frmer Research Assistant at Nrth Carlina State University nw with the Institute f Fd and Agricultural Science, Agricultural Research Educatin Center, 700 Experiment Statin Rad, Lake Alfred, Flrida 33850. Paper N. 7047 f the Jurnal Series f the Nrth Carlina Agricultural Research Service, Raleigh, Nrth Carlina 27650. Presented at the Annual Meeting f the Eastern Sectin, American Sciety f Enlgists, 8 August 1980, Erie, Pennsylvania. Manuscript submitted 28 August 1981. Revised manuscript received 17 February 1982. Accepted fr publicatin 22 February 1982. Chemical and physical changes ccurring in the berries f tw cultivars (Carls and Nble) f muscadine grapes (Vitis rtundiflia) were fllwed during the grwing seasn. The same chemical and physical determinatins were made n the berries f fur additinal muscadine cultivars samples nly at their nrmal harvest date. The fllwing chemical r physical character- ABSTRACT istics were significantly crrelated with berry maturatin in bth cultivars: berry weight, seed weight, percent misture, Brix, titratable acidity, Brix-acid rati, ph, fructse, glucse, sucrse, tartaric acid and malic acid. Best fit regressin equatins were calculated and used t describe the relatinship f a given chemical r physical characteristic with berry maturatin. While cnsiderable infrmatin exists abut changes in chemical cmpsitin f Vitis vinifera grapes during maturatin (2), there is cmparatively little infrmatin abut changes in physical and chemical prperties f muscadine grapes (Vitis rtundiflia). Muscadine is the cmmercially imprtant grape species f the Sutheastern United States. Carrll et al. (8) measured the sugars, rganic acids, ph, titratable acidity, and sluble slids in 12 cultivars f muscadine grapes at maturity fr three cnsecutive seasns. Tartaric and malic were the principal rganic acids and fructse, glucse, and sucrse were the majr sugars. Significant variatin was fund in acid and sugar cncentratins fr all cultivars between years, pssibly due t seasnal variatins in degree-day heat accumulatin. Jhnsn and Carrll (9) measured changes in the majr sugars and acids in Scuppernng (V. rtundiflia) grapes during maturatin. Malic acid reached a maximum cncentratin early in the grwing seasn, became the predminant rganic acid near v~raisn, and then declined in cncentratin until harvest. Tartaric acid decreased steadily frm initial sampling date until harvest. Fructse, glucse, and sucrse were the principal sugars accunting fr mre than 90 % f the ttal sugars present in bth ripe and unripe stages f Scuppernng grapes. Glucse was the predminant sugar at earlier The use f trade names in this publicatin des nt imply endrsement by the Nrth Carlina Agricultural Research Service f the prducts named, nr criticism f similar nes nt mentined. 168 stages f berry develpment. Glucse and fructse cncentratins equalized with further berry develpment, then fructse became the sugar fund in highest cncentratin in Scuppernng grapes at maturity. This pattern f changing sugar cncentratin has been demnstrated in V. vinifera grapes (13). Sucrse was fund in significant amunts (10-20~i,) in Scuppernng grapes (9). While sucrse has been reprted in cultivars f V. labrusca (7), nly trace amunts have been fund V. vinifera grapes (1). In a recent study (16), Marcy et al. fllwed and characterized changes in the free amin acid cntents f Carls and Nble muscadine grapes during maturatin. In general, the free amin acid cntents f the muscadines were similar t thse reprted in the literature fr V. vinifera and V. labrusca cultivars. The purpse f this study was t measure imprtant physical and chemical changes in Carls and Nble muscadine grapes during maturatin. Carls, a lightskinned grape, is the predminant cmmercial grape cultivar in Nrth Carlina and Nble is a leading darkskinned cultivar. MATERIALS AND METHODS Sample selectin: All grapes used in this study were harvested in 1978 frm healthy, five-year-ld vines grwing at the Nrth Carlina Experiment Statin in Clintn, Nrth Carlina. The vines were cultivated accrding t recmmended practices (6), and trained t the Geneva-Duble-Curtain system. Tw cultivars, Car-

MATURATION OF MUSCADINE GRAPES- 169 ls and Nble, were sampled frm an immature stage thrugh ripeness t verripeness. Tw light-skinned cultivars, Magnlia and Dixie and tw dark-skinned cultivars, Regale and Pride, were samples nly at nrmal harvest date. Sample selectin and ther related details have been described in a recent publicatin (16). Physical measurements and percent misture: Berry and seed weights were determined n duplicate 100 cunt berry samples using a tp-lading balance. Berry diameter was measured at the widest pint with calipers n duplicate 10 cunt berry samples. Percent misture was determined by ven drying f hmgenized berry samples accrding t AOAC (4). Sluble slids, ph, titratable acidity: Sluble slids, ph and titratable acidity were measured by the usual methds (9) n juice fractins which were prepared frm subsamples f the berries. Individual sugars and rganic acids: Harvested berries were chilled t 4 C and deseeded while cld. Deseeded samples were frzen immediately and stred at -20 C until analysis culd be cmpleted. Fr analysis, the partially thawed berries were hmgenized in a Waring blender fr ne minute at high speed. A 20 g sample f hmgenized berries and 100 ml f biling water were added t a 250 ml beaker, cvered with a watch glass and heated t apprximately 100 C fr 20 minutes. The mixture was filtered int a 250 ml vlumetric flask and was brught t vlume. As a check f the extractin prcess, the residue f every tenth sample was reextracted and analyzed (the extractin prcess was 99 + % effective). Vlatile trimethysilylated (TMS) derivatives f the sugars and rganic acids were prepared and analyzed as described in a cmpanin paper by the authrs (15). A cmputer data acquisitin system was used t integrate sugar and rganic acid chrmatgrams by cmparisn t knwn and internal standards. Ttal phenls: Duplicate 10 ml samples f the extract used fr sugar and acid determinatins were analyzed fr ttal phenls by the Flin-Cicalteu prcedure (3). Statistical analysis: All data were subjected t linear and nn-linear mdeling using Statistical Analysis System (5) t determine relatinships between chemical and physical prperties f the grape and sampling date. 50-- 40-- 30-- 20-- 10-- 0 60--... TARTARIC ACID... MALIC ACID SUCROSE - - - - " " - GLUCOSE,~"~".... FRUCTOSE ~ ~, s~.,z. L:.... I I I JUL AUG SEPT... TARTARIC ACID... MALIC ACID SUCROSE 50-- - - - - - - - - GLUCOSE i p.... FRUCTOSE -I-,T, 4- ' w cl 30-- U.l IJJ I I I~ 20--", ~'''~'4, E 10-- ~ ~~ ',-2" I I I ' I JUL AUG SEPT OCT Fig. 1. Best fit mdels fr changes in sugars and rganic acids in Carls and Nble grapes during maturatin. Table 1. Charges in sugars and rganic acids (mgg fresh weight) f Carls and Nble grapes. 714 721 83 811 815 818 822 825 829 831 95 98 913 916 923 101 Malic acid 13.27 11.58 11.83 8.84 7.13 6.41 4.81 6.53 4.14 3.67 3.79 3.58 2.45 2.11 2.63 Tartaric acid 17.33 15.13 14.07 11.44 10.42 9.66 7.58 11.68 9.01 9.16 8.69 8.31 8.75 6.74 9.12 Fructse 2.95 4.86 9.98 15.81 26.65 38.41 38.89 31.83 29.63 39.93 32.02 43.92 40.87 37.08 42.19 Glucse 7.15 9.11 13.23 17.46 26.61 35.99 34.99 31.54 30.76 39.76 30.23 39.76 36.62 33.48 35.18 Sucrse 0.38 0.65 1.28 3.23 2.77 6.67 3.85 4.65 3.52 9.74 8.94 10.87 15.04 14.45 17.78 Malic acid 10.50 11.08 11.52 8.33 6.60 5.88 4.07 3.13 3.43 2.01 0.95 0.88 0.00 0.59 0.00 0.00 Tartaric acid 21.07 22.13 15.61 12.88 11.41 11.53 8.81 10.22 11.89 9.23 7.21 9.14 8.27 7.65 9.15 8.68 Fructse 2.92 3.84 7.70 13.64 25.77 27.28 31.77 36.98 33.09 37.43 38.19 43.49 40.86 42.45 51.60 46.37 Glucse 7.45 9.64 11.79 17.51 26.85 28.63 30.73 36.27 31.94 35.17 34.72 39.04 36.28 38.08 44.01 49.77 Sucrse 3.02 1.17 1.54 1.34 5.94 9.95 12.08 7.83 18.00 21.85 19.40 19.63 25.25 32.01 29.89 34.93

170- MATURATION OF MUSCADINE GRAPES RESULTS AND DISCUSSION Changes in individual sugars and acids in Carls and Nble muscadine grapes during ripening are given in Table 1, with best-fit regressin curves f these data shwn in Figure 1. As expected, ttal sugar cncentratin increased with berry maturity and ttal acid cncentratin decreased. Sucrse was fund t cntribute significantly t the ttal sugars present in muscadine grapes at maturity (Tables 1 and 2) which agrees with previus findings (8,9). In Nble and Carls berries, sucrse accunted fr 25% and 17%, respectively, f ttal sugars present. Glucse was fund in larger amunts than fructse in the mature stage f berry develpment. At a later stage f berry develpment, the tw sugars became apprximately equal in cncentratin. Slightly mre fructse than glucse was present in the ripest samples. This als agrees with previus findings (9,11). In Carls, the sugar t acid rati was slightly better crrelated with maturity (r = 0.982) than was titratable acidity (r = 0.974) r sluble slids (r = 0.974). In Nble, this rati was better crrelated with maturity (r = 0.978), than was sluble slids (r = 0.966) but nearly identical t that f titratable acidity (r = 0.979). Since utilizatin f the grape is dependent n bth ttal sluble slids and titratable acidity, the sugar t acid rati shuld be a useful indicatr f ptimum harvest date fr muscadine grapes. Magnlia, Regale and Pride (Table 2) shwed prprtins f sugars similar t Carls and Nble at nrmal harvest date (Tables 1 and 3). Dixie had sucrse as its mst prevalent sugar at maturity accunting fr 36.5% f the ttal sugar. This, as well as the lwest titratable acidity (Table 2) f any cultivar in the study, explains the very sweet flavr (17) f this cultivar. Tartaric acid was the principal rganic acid at all sampling dates and fr all cultivars (Tables 1 and 2). While bth tartaric and malic acids decreased with maturity, the decrease in malic acid was mre prnunced. Maximum cncentratin f malic acid in Scuppernng grapes was reprted t be mid-seasn just prir t v~raisn (9), which was nt fund in either cultivar in Table 2. Chemical and physical characteristics f fur cultivars f muscadine grapes sampled at nrmal harvest date. Cultivar Characteristic Magnlia Dixie Regale Pride Malic acid a 0.90 2.14 0.34 2.56 Tartaric acid a 7.31 5.73 8.70 7.84 Fructse a 47.40 54.27 48.10 40.33 Glucse a 36.08 47.23 43.35 38.52 Sucrse a 25.49 58.28 22.31 20.00 Titratable acidityb 0.74 0.62 0.83 0.73 Sluble slids c 13.05 16.35 13.30 13.30 ph 3.29 3.65 3.25 3.45 Ttal phenls d 1.71 1.84 3.12 1.61 Percent misture 85.78 79.72 84.68 85.30 Berry weight e 5.77 4.61 5.12 8.27 Seed weight f 0.64 0.30 0.29 0.35 Berry diameter h 2.18 1.98 2.01 2.31 amgg deseeded weight bmg tartaric acidg deseeded weight cdegree Brix dmg gallic acidg deseeded weight egrams (average f 100 berries) fgberry (average f 100 berries) hcm (average f 10 berries) this study. The malic acid cncentratin f grapes (V. vinifera) is strngly influenced by temperature during the grwing seasn (10). During the grwing seasn f this study, heat accumulatin frm May thrugh September was 4130 degree days measured as described by Amerine et al. (2). Carrll et al. (9) reprted heat accumulatin f 2336 t 2815 degree days when measured frm day f blm t day f harvest during a three year study. The higher amunt f heat accumulatin during the grwing seasn f this study shuld partially explain lwer titratable acidity and higher sluble slids than previusly reprted. The higher amunt f degree days als may explain lwer amunts f malic acid fund than that previusly reprted (9). Cultivar differences are als a cntributing factr. In Carls, malic acid shwed a threefld decrease n a per berry basis frm the immature stage (933 mg berry) t the mature stage (311 mgberry), while tartaric acid cncentratin remained nearly cnstant n a per berry basis at 43 mgberry. A similar pattern fr bth acids was seen in Nble berries. The decrease in tartaric Table 3. Changes in chemical cnstituents f Carls and Nble grapes during maturatin. 7!4 721 83 811 815 818 822 825 829 831 95 98 913 916 923 101 ph 2.77 2.89 2.87 2.92 3.15 3.14 3.20 3.13 3.17 3.28 3.27 3.31 3.23 3.40 3.40 Titratable acidity a 30.00 30.00 28.90 28.00 15.60 15.30 13.60 14.30 13.50 9.80 10.00 10.50 8.30 7.50 7.80 Sluble slids b 3.55 4.00 5.20 5.85 8.25 10.15 9.90 9.10 10.25 11.60 12.15 12.55 12.40 13.15 15.00 Ttal phenls c 2.29 2.33 2.38 2.18 1.79 1.81 2.13 1.54 1.75 1.86 2.14 2.31 1.84 1.97 2.04 Percent misture 92.66 92.74 91.78 90.65 89.98 89.43 88.67 88.08 87.27 86.86 85.84 85.24 84.28 83.74 82.60 ph 2.88 2.86 3.00 2.95 3.04 3.16 3.22 3.20 3.37 3.43 3.48 3.43 3.51 3.62 3.70 3.50 Titratable acidity a 28.40 30.20 27.10 22.90 17.40 14.70 14.30 12.60 10.00 6.60 7.80 7.60 6.60 6.10 6.70 6.90 Sluble slids b 3.60 3.90 4.30 5.00 7.50 9.75 10.40 9.55 12.05 12.30 12.70 13.10 12.05 14.05 15.65 16.05 Ttal phenls c 2.01 2.83 2.14 1.68 1.42 1.78 1.83 2.04 1.92 1.82 2.78 2.65 2.45 2.02 3.12 3.63 Percent misture 92.44 92.82 91.91 90.60 89.81 89.18 88.30 87.63 86.84 86.31 85.26 84.68 83.82 83.39 82.70 82.58 aexpressed as mg tartarateg deseeded weight. bdegree Brix. CExpressed as mg gallic acidg deseeded weight.

MATURATION OF MUSCADINE GRAPES ~ 171 5-- 4-- ) 3E <[-la:. 5- (.9 2- -"--- BERRY WT ---- BERRY WT -'--" p H ph J I I 20~ ca 15~._1 t~ w IO-- _1 ID..I O () 5-- f SOLUBLE SOLIDS =~, ---- I I I I 1 I 1 1 95-- PERCENT MOISTURE TITRATABLE ACIDITY 40-- =--- -'-"-... 90-- --'---'- cat 30--.} _ < w 85-- u : ca 20- < w I-- ca tl.i <[ w I- u~ "~ IO-- \N\N E 80 I! I I I I I JULY AUG SEPT OCT Fig. 2. Best fit mdels fr changes in chemical and physical prperties f Carls and Nble grapes during maturatin. Table 4. Crrelatin and partial regressin cefficients fr best fit mdeling f Carls and Nble grape characteristics with maturity. Carls Crrelatin Crrelatin Characteristic cefficient Intercept b ix b2x2 cefficient Intercept b 1X b2x2 Malic acid 0.964** 12.973-0.005-0.0076 0.975** 10.618 0.174-0.012 Tartaric acid 0.908** 17.378-0.211-0.0004 0.936** 22.878-0.338 0.0014 Fructse 0.882** 0.929 0.414 0.0173 0.942** 1.593 0.091 0.0237 Glucse 0.881 ** 6.029 0.213 0.0191 0.935** 5.244 0.525 0.0029 Sucrse 0.951 ** 0.413 0.024 0.0008 0.947** 4.036-0.663 0.0284 Ttal phenls 0.425 Ns 2.371-0.007-0.0002 0.783** 2.498-0.037 0.0005 Titratable acidity 0.974** 3.066 0.005-0.0018 0.979** 2.918-0.015 0.0008 Sluble slids 0.974** 3.362 0.043 0.0039 0.966** 3.491-0.041 0.0069 % Misture 0.968** 92.615 0.056-0.0053 0.974** 92.358 0.114-0.0078 Berry weight 0.956** 2.519-0.004 0.0020 0.983** 1.270 0.000 0.0012 Berry diameter 0.800* 0.467 0.015-0.0002 0.607 Ns 0.779-0.020 0.0005 Seed weight 0.752* 0.336-0.001 0.0001 0.742** 0.237-0.001 0.0001 ph 0.933** 2.810 0.003 0.0002 0.972** 2.914-0.014 0.0007 *= significant at.05 level. **= significant at.01 level. NS= nn significant at.05 level. Nble

172 -- MATURATION OF MUSCADINE GRAPES Table 5. Changes in physical characteristics f Carls and Nble grapes during maturatin. 714 721 83 811 815 818 822 825 829 831 95 98 913 916 923 101 Berry weight a 2.48 2.70 2.68 3.40 3.97 4.41 4.15 4.19 4.31 4.46 4.36 5.10 5.20 5.21 4.71 Seed weight b 0.34 0.34 0.28 0.32 0.36 0.41 0.39 0.36 0.35 0.37 0.40 0.38 0.38 0.40 0.45 Berry diameter c 1.62 1.70 1.75 1.91 1.96 2.01 1.96 1.93 2.01 2.01 1.91 2.06 2.08 1.98 1.96 Berry weight a 1.52 1.09 1.29 1.83 2.17 2.44 2.80 3.06 3.40 3.55 3.86 4.00 4.12 4.11 3.81 3.89 Seed weight b 0.23 0.23 0.23 0.24 0.23 0.24 0.23 0.24 0.31 0.25 0.26 0.26 0.26 0.27 0.28 0.28 Berry diameter c 1.40 1.45 1.45 1.50 1.60 1.60 1.65 1.65 1.70 1.73 1.65 1.70 1.75 1.73 1.75 1.73 ag per berry (average f 100 berries). bg seeds per berry (average f 100 berries). Ccm (average f 10 berries). acid cncentratin appears t be the result f dilutin as the berry expanded, while malic acid appears t be bth diluted and respired as has been fund in V. vinifera grapes (14). As expected, an increase in ph fllwed the decrease in titratable acidity during maturatin f Carls and Nble berries (Fig. 2). Changes in ttal phenls (Table 3) were erratic during berry maturatin, which agrees with bservatins n V. vinifera grapes (18). The cncentratin f ttal phenls in V. vinifera was subject t dramatic changes within shrt perids, and it was cncluded these changes resulted frm envirnmental factrs rather than being a functin f maturity (18). This is supprted in this study by variable results and nn-significant relatinships between maturity and ttal phenls (Table 4). There was a significant decrease in percent misture f Carls and Nble berries during maturatin (Tables 3 and 4). Because f its highly significant crrelatin with maturity and ease f testing, the use f percent misture as an adjuctive index f maturity has merit. Berry weight f bth cultivars reached a maximum value n r befre the nrmal harvest date and then declined in weight t the verripe harvest date (Fig. 2). A similar trend in Scuppernng berry weight was bserved (9). Kliewer (11) reprted that V. vinifera grapes reached their maximum weight per berry apprximately ne week befre being fully ripe. If yield can be maximized withut an ffsetting lss f quality, then the perid f maximum berry weight wuld be the ptimal harvest date t maximize yield n a tns per acre basis. Berry diameter was nt crrelated with maturity during the sampling perid in Nble berries, althugh there was a significant increase in berry diameter in Carls berries (Tables 4 and 5). Seed weight increased in bth cultivars and was crrelated with maturity (Tables 4 and 5). Percent seed weight at full maturity ranged frm 4.2% in Pride berries t 11.1% fr Magnlia berries. Nble and Carls berries had 7.4% and 9.6% seed weight, respectively, at full maturity. Many chemical and physical characteristics f the muscadine cultivars studied were highly crrelated with maturity. Knwledge f these relatinships can be utilized in predicting and ptimizing yield, and in maximizing quality f fermented and unfermented prducts. LITERATURE CITED 1. Amerine, M. A. Cmpsitin f wine. 1. Organic cnstituents. Adv. in Fd Res. 5:353 (1954). 2. Amerine, M. A., H. W. Berg and W. V. Cruess. The cmpsitin f grapes. In "Technlgy f Wine Making." 3rd ed. AVI Publishing C., Westprt, Cnn. (1972). 3. Amerine, M. A. and C. S. Ough. "Wine and Must Analysis." Jhn Wiley and Sns, Inc. New Yrk, New Yrk (1973). 4. AOAC. "Official Methds f Analysis." 12th ed. Assciatin f Analytical Chemists. Washingtn, D.C. (1976). 5. Barr, A. J., J. H. Gdnight, J. P. Sail, and J. T. Helwig. A User's Guide t SAS 76. Sparks Press, Raleigh, N.C. (1976). 6. Brks, J. F. Muscadine Prductin Guide fr Nrth Carlina. Nrth Carlina Agricultural Extensin Service, Raleigh, N.C. (1975). 7. Caldwell, J. S. Sme effects f the seasnal cnditins upn the chemical cmpsitin f American grape juices. J. Agr. Res. 30:1133 (1925). 8. Carrll, D. E., M. W. Hver, and W. B. Nesbitt. Sugar and rganic acid cncentratin in cultivars f muscadine grapes. J. Amer. Sc. Hrt. Sci. 96:737 (1971). 9. Jhnsn, L. A., and D. E. Carrll. Organic acid and sugar cntents f Scuppernng grapes during ripening. J. Fd Sci. 38:21 (1973). 10. Kliewer, W. M. Influence f envirnment n metablism r rganic acids and carbhydrates in Vitis vinifera. I. Temperature. Plant Physil. 39:869 (1964). 11. Kliewer, W. M. Changes in cncentratin f malates, tartrates, and ttal free acids in flwers and berries f Vitis vinifera. Amer. J. Enl. Vitic. 16:93 (1965). 12. Kliewer, W. M. Sugars and rganic acids f Vitis vini[era. Plant Physil. 41:923 (1966). 13. Kliewer, W. M. The glucse-fructse rati f Vitis vinifera grapes. Amer. J. Enl. Vitic. 18:33 (1967). 14. Kliewer, W. M. Effect f temperature n the cmpsitin f grapes grwn under field and cntrlled cnditins. Am. Sc. Hrt. Sic. 93:797 (1969). 15. Marcy, J. E. and D. E. Carrll. Research nte: A rapid methd fr the simultaneus determinatin f rganic acids and sugars in grape musts. Amer. J. Enl. Vitic. 33:176-7 (1982). 16. Marcy, J. E., D. E. Carrll and C. T. Yung. Changes in free amin acid and ttal nitrgen cncentratins during maturatin f muscadine grapes (V. rtundiflia). J. Fd Sci. 46:543-547 (1981). 17. Nesbitt, W. B., V. H. Underwd and J. A. Mrtensen. 'Dixie' Grape. Hrt. Science 11:520 (1976). 18. Singletn, U. L. and P. Esau. "Phenlic Substances in Grapes and Wine, and Their Significance." Adv. Fd Res. Supplement I. Academic Press, New Yrk, New Yrk (1969).