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Twenty-six muscadine grape (Vitis rotundifolia Michx.) cultivars and selections were evaluated for a range of skin and flesh texture attributes. Two Vitis vinifera L. and one Vitis labruscana Bailey table grape cultivars were included for comparison. Penetration tests using a flat cylindrical probe were used to assess whole berry texture. Ideal whole berry texture is firm and easily broken down during mastication, which was measured as small berry deformation at first peak and berry maximum force, respectively. Muscadine berry deformation at first peak ranged from 4.35 to 7.82 mm and berry maximum force ranged from 5.7 to 13.9 N. V. vinifera table grape berries were firmer (3.14 to 3.19 mm berry deformation at first peak) and more tender (4.0 to 4.9 N berry maximum force) than muscadine berries. Berry penetration work was strongly correlated with both berry deformation at first peak and berry maximum force and ranged from 13.0 to 54.1 mJ in the muscadine germplasm. Penetration tests of muscadine berry flesh revealed a range of flesh firmness from very soft (0.65 N) to firm (3.06 N) but none was as firm as the V. vinifera berry flesh (3.9 N). Penetration tests of muscadine berry skins revealed newer selections bred for table use had relatively tender skins with a skin break force of 12.1 N, which was not different from V. vinifera samples. Berry penetration work and flesh maximum force were determined to be the most useful characteristics for routine screening of breeding program material. The genus Vitis L. contains two subgenera, Euvitis Planch. (bunch grapes) and Muscadinia Planch. (muscadine grapes). The muscadine grape is the only commonly cultivated member of the Muscadinia subgenus. Muscadines are native to the southern United States and have been cultivated for over 400 years (Lane, 1997). Muscadines grow in regions where winter temperatures remain above –12 C. The muscadine grape differs from the familiar bunch grape (Vitis labrusca L., V. vinifera, and their various hybrids) by the presence of smaller clusters, unbranched tendrils, and berries with thick skins and a unique fruity aroma. In addition, muscadine berries often abscise from the cluster when ripe and are picked as single berries and sold in plastic containers much like other berries. Although they enjoy popularity within their region of adaptation, muscadine grapes are not well known outside of the southeastern United States. To increase consumption of fresh market muscadines, they need to be successfully introduced to consumers unfamiliar with the fruit. Consumer acceptance of muscadine fruit has likely been hampered by the relatively tough skins and soft flesh of muscadine berries. These traits are especially pronounced in comparison with V. vinifera table grapes, which have been selected for their tender skins and a crisp pulp. Consumers in the southern United States are less troubled by these attributes and either discard the skins or consume the skins of the more tender-skinned cultivars. However, to successfully market muscadines to consumers only familiar with V. vinifera table grapes, new muscadine cultivars with textural attributes more akin to V. vinifera table grapes will likely need to be developed. Texture is one of the most important quality characteristics of fresh-market grapes (Sato et al., 1997). Texture includes all physical characteristics sensed by touch, which are related to deformation under applied force, and can be measured objectively in terms of force, distance, and time (Letaief et al., 2008). Sensory attributes such as skin friability, skin thickness, and flesh firmness have been proposed to characterize commercial table grape cultivars (Cliff et al., 1996). Recently, mechanical investigation into grape texture has been recommended to replace sensory panel studies because mechanical tests can be conducted under controlled laboratory conditions making them more stable than sensory tests and easier to carry out (Rolle et al., 2011). The mechanically measured variables most often used to define texture are force and deformation (distance), and various machines have been designed to carry out these tests (Sato and Yamada, 2003). Berry texture characteristics are most commonly investigated through the use of a universal testing machine that produces force deformation curves (Rolle et al., 2012). A crisp pulp is particularly desired among consumers of table grapes, and this trait is often associated by consumers with freshness of the product. Crispness may be defined as the sensual experience of eating a food item that fails in a brittle manner under a relatively low force (Vincent, 2004). This is in contrast to ‘‘jelly,’’ which has low work to fracture (brittle) but is so soft that it deforms a long way before fracture, and ‘‘tough,’’ which has higher work to fracture but is soft and deforms easily. The difficulty in mastication of V. labruscana grape flesh may contribute to its comparatively small consumption as a table grape in comparison with V. vinifera (Bourne, 1979). Sato et al. (1997) showed differences in grape berry texture as measured by flesh puncture tests using a texture analyzer. Difficulty of mastication of the flesh in sensory tests was found to be highly correlated to deformation at first peak (distance traveled by the probe between contact with the sample and first breakdown of the sample). Flesh firmness in the sensory test was best described by the maximum force reached before sample breakdown. V. vinifera cultivars with a crisp flesh had a small deformation at first peak and large maximum force. V. labruscana cultivars had a wide range of flesh textures varying from tough (large deformation at first peak and maximum force) to tender (small deformation at first peak and maximum force) (Sato et al., 1997). Further tests indicated that V. vinifera table grape cultivars had lower deformation at first peak and higher maximum force scores than did wine-use or dual-purpose cultivars (Sato and Yamada, 2003). Textural analysis of the skins of grape berries has been done in both wine grape and table grape V. vinifera cultivars (Rolle et al., 2012). Berry skin break force and energy can be used to differentiate wine grape varieties (Giacosa et al., 2012; Rio Segade et al., 2008). Rolle et al. (2011) found that the textural profile attributes of hardness, gumminess, and chewiness were best described by skin break force, skin break energy, and modulus of elasticity in white table grape cultivars. Skin break force was particularly useful in differentiating among V. vinifera table grape cultivars and ranged from 0.329 N to 0.585 N (Rolle et al., 2012). Ideal grape skins will be highly friable but with sufficient toughness to protect the berry from pathogens, harvest damage, and splitting and cracking on the vine. Puncture tests have also been shown to be helpful in predicting the anthocyanin extractability of grape skins in ‘Nebbiolo’ and ‘Brachetto’ berries (Rolle et al., 2008). Textural analysis of muscadine grapes has been limited. Walker et al. (2001) used a flat 2-mm cylindrical probe to penetrate unpeeled ‘Fry’ muscadine berry halves to evaluate fruit firmness in different berry maturity classes and during storage. Firmness was found to decline with increasing maturity and storage times. Development of improved texture in muscadine grapes has been hampered by the lack of a standardized protocol for textural analysis. Our objectives were to express muscadine grape texture by instrumental analysis and to evaluate berry texture in a wide range of muscadine germplasm. Materials and Methods Plant material. Muscadine and the V. labruscana cultivar Blue Lake berries were Received for publication 7 June 2013. Accepted for publication 29 June 2013. To whom reprint requests should be addressed; e-mail pconner@uga.edu. 1130 HORTSCIENCE VOL. 48(9) SEPTEMBER 2013 sampled in 2012 from vines grown at the University of Georgia (UGA)–Tifton Campus located in Tift County, GA. (lat. 33 53#7.69$ N, long. 83 25#20.30$ W). Muscadine clones used in this work were a mixture of historical and new cultivars, as well as advanced selections from the UGA breeding program and represented a wide range of skin and flesh texture and a mixture of table and juice germplasm. All vines were trained to a single wire trellis with two cordons per vine and spaced 3 m between plants within the row and 4.5 m between rows. Vines were irrigated through a single line with a 3.6-L·h drip emitter located 30 cm from each side of the vine. Diseases and insects were controlled according to commercial guidelines (Poling et al., 2003). All muscadine and the ‘Blue Lake’ samples were collected at their ripening time by removing entire clusters by hand from vines. To avoid creating detachment tears, berries were separated from bunches by cutting the stems so that the pedicel remained attached to the berry. Samples were brought indoors to equilibrate to room temperature (22 C). ‘Sugraone’ and ‘Midnight Beauty’ V. vinifera berries were purchased from a local supermarket. Muscadine berries were density-sorted by floating them in sodium chloride brine solutions of 8% to 11% (Lanier and Morris, 1979). Fruit was placed into 8% brine and berries that floated were removed, rinsed with tap water, dried, and designated as density grade 1. This procedure was repeated with 9%, 10%, and 11% brine to give density grades 2, 3, and 4, respectively. The effect of density grade on texture characteristics was investigated using all four density grades of ‘Triumph’ muscadine berries, but all other experiments only used density grade 2 berries. Textural analysis. An Universal Testing Machine TaxT2i Texture Analyzer (Stable Micro System, Godalming, Surrey, U.K.) equipped with a 25-kg load cell was used. Sample size was 20 berries for each clone examined. Force and distance values were read directly from the electronic keyboard controlling the analyzer. Probe type and speed and tri

Instrumental Textural Analysis of Muscadine Grape Germplasm