Peaches stored in air for 40 days at OC developed severe internal breakdown and poor quality after transferring them to 20C to ripen. Comparable fruit stored under controlled atmosphere (1% O2 + 5% CO2) and then ripened at 20C had no breakdown and retained good quality. Fruit stored under CA had less reducing sugars but more sucrose than air stored fruit. Fruit pH increased and titratable acidity decreased over a 40 day storage period. Citric acid increased slightly while malic acid decreased during storage. Little or no differences in overall acidity and individual organic acids existed between CA and air storage. Little or no change in individual phenolic acid content occurred during storage or between CA and air storage. Internal color darkened and became redder with storage. CA stored fruit was significantly firmer than air stored fruit. Sensory evaluation indicated CA stored fruit was more acidic, sweeter, and had better overall flavor than air stored fruit.
Ahmed F. El-Shiekh and David H. Picha
Malkeet S. Padda and David H. Picha
Three different style fresh-cut (shredded, French fry, and sliced) sweetpotatoes [Ipomoea batatas (L.) Lam.] were stored at 0 and 5 °C for 4 and 8 days. At specified storage intervals, the fresh-cut sweetpotatoes were analyzed for total phenolics, individual phenolic acids, and antioxidant activity. Sweetpotato tissue analyzed immediately after cutting was considered the control. Storage at 5 °C resulted in an increase in total phenolics in all types of fresh-cut sweetpotatoes, except in shredded tissue analyzed after 4 days of storage. However, at 0 °C, only sliced tissue accumulated higher total phenolics than the control. In general, antioxidant activity in all fresh-cut sweetpotatoes held at 5 °C was higher than in the control. No significant increase in antioxidant activity was observed in shredded sweetpotatoes stored at 0 °C. Chlorogenic acid followed by 3,5-dicaffeoylquinic acid were the predominant phenolic acids present in fresh-cut sweetpotatoes. The highest content of chlorogenic acid (539.9 μg·g−1 dry weight) in sliced tissue stored for 8 days at 5 °C was ≈6-fold higher than in the control (88.3 μg·g−1 dry weight). No significant development of tissue browning, off-odors, or off-flavors were observed after 8 days of storage and the products were considered to be marketable.
Malkeet S. Padda and David H. Picha
Phenolic compounds and antioxidant activity were quantified in the principal sweetpotato cultivars marketed in the European Union. Total phenolic content, individual phenolic acids, and antioxidant activity in each cultivar were determined using Folin-Denis reagent, reversed-phase HPLC, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) methods, respectively. Significant differences in phenolic composition and antioxidant activity were found between cultivars. A Jamaican-grown, white-fleshed cultivar had the highest total phenolic content [4.11 mg·g-1 chlorogenic acid (dry tissue weight)], while the highest antioxidant activity [3.60 mg·g-1 Trolox (dry tissue weight)] was observed in the orange-fleshed California-grown cultivar Diane. Chlorogenic acid and 3,5-dicaffeoylquinic acid were the predominant phenolic acids, while caffeic acid was the least abundant in most cultivars. The highest content of chlorogenic acid (0.42 mg·g-1 dry tissue weight); 3,5-dicaffeoylquinic acid (0.43 mg·g-1 dry tissue weight); and 3,4-dicaffeoylquinic acid (0.25 mg·g-1 dry tissue weight) was present in the white-fleshed Jamaican cultivar. The orange-fleshed cultivars Diane and Beauregard had the highest content of caffeic acid (0.13 mg·g-1 dry tissue weight) and 4,5-dicaffeoylquinic acid (0.32 mg·g-1 dry tissue weight), respectively.
Anthony Kilili, David H. Picha, and Yuehe Huang
`Beauregard' sweetpotatoes (Ipomoea batatas L. Lam) were stored under a continuous flow of 0%, 1%, 1.5%, 2%, 5%, 10%, or 21% O2 (balance N2) for 14 days. Respiration rate was significantly lower at 1.5%, 2%, 5%, and 10% O2 compared with 21% O2, while respiration at 0% and 1% O2 was higher than at 1.5%, 2%, 5%, and 10% O2. Respiration rate at 0% O2 remained high for several days after exposure to air while that at 1.5%, 2%, 5%, and 10% O2 increased rapidly to equal that of 21% O2. Ethanol and acetaldehyde accumulated rapidly at 0% and 1% O2 but were lower at the other O2 levels. Ethanol increased 16- and 4-fold after 14 days of storage at 0% and 1% O2, respectively, compared to 21% O2. In addition, acetaldehyde increased 11- and 8-fold at 0% and 1% O2 respectively, compared to 21% O2. Sucrose and total sugar concentration increased under low O2 concentration while reducing sugars (fructose and glucose) and pH decreased.
Don R. LaBonte and David H. Picha
Six sweetpotato cultivars were evaluated for changes in individual sugar concentration, dry weight, and alcohol insoluble solids (AIS) during growth and development. Measurements were taken at weekly intervals from 7 to 21 weeks after transplanting. Sucrose, the major sugar during all stages of development, generally increased in concentration throughout development for `Heart-o-gold', `Travis', and `Jewel', but peaked at 17 weeks for `Beauregard' and `Whitestar'. The high-dry matter white flesh cultivars of `Rojo Blanco' and `Whitestar' contained the lowest sucrose concentration. The monosaccharides glucose and fructose generally decreased in concentration up to 17 weeks in 4 of 6 cultivars, followed by an increase from 17 to 21 weeks in all cultivars. Glucose concentration was marginally greater than fructose at all stages of development in each cultivar. Little or no increase in total sugar concentration occurred during development in `Whitestar' and `Rojo Blanco'. A substantial increase in total sugars occurred during development with `Jewel', `Beauregard', `Heart-o-gold' and `Travis'. Cultivars differed widely in their individual sugar concentrations during development. Percent dry matter increased in all cultivars from 7 to 14 weeks. Dry matter and AIS decreased during the later stages of development.
Wilmer A. Barrera and David H. Picha
Sweetpotato is considered a good source of ascorbic acid (vitamin C) and certain B vitamins. These water-soluble vitamins (WSV) play essential roles in sustaining human health. Besides the root, sweetpotato vegetative tissues are also edible and considered high in nutritional value. Despite the availability of general reference values for sweetpotato WSV content in the root and leaves, little is known about the distribution of these vitamins in specific sweetpotato root and vegetative tissues. The objective of this study was to determine the ascorbic acid (AA), thiamin (B1), riboflavin (B2), and vitamin B6 content in a range of foliar tissues including buds, vines, young petioles, young leaves, mature petioles, and mature leaves and root tissues including the skin, cortex, and pith tissue at the proximal, distal, and center regions of the root. Among foliar tissues of ‘Beauregard’ sweetpotatoes, the AA content was highest in young leaves (108 to 139 mg/100 g fresh weight) and lowest in mature petioles (7.2 to 13.9 mg). No thiamin was detected in foliar tissue, whereas mature leaves contained the highest riboflavin and vitamin B6 content (0.22 to 0.43 mg and 0.52 to 0.58 mg, respectively). In root tissues of ‘Beauregard’ and ‘LA 07-146’ sweetpotatoes, the AA content was lower in the skin (1.9 to 5.6 mg and 2.54 to 3.82 mg, respectively). The AA content in the cortex and pith tissue at the proximal, distal, and center of the root was generally similar. The thiamin content was variable among root tissues, whereas the skin contained the highest riboflavin content and the lowest vitamin B6 content across root tissues of both cultivars. The results of this study confirmed earlier reports suggesting that sweetpotato leaves can be a good source of multiple WSV in the human diet.
Y.H. Huang, David H. Picha, and Charles E. Johnson
The glucose-6-phosphate dehydrogenase (G-6-PDH) and glucose oxidase methods are commonly adapted for plant invertase assay. A disadvantage of the G-6-PDH assay is the relatively high cost of the coupling enzymes and cofactors. A disadvantage of the glucose oxidase method, which uses a glucose kit (Sigma, 510-A), is the presence of high activities of acid invertase and alkaline invertase in the PGO enzyme formula (peroxidase and glucose oxidase), which gives a falsely high invertase activity value. An alternative and inexpensive coupled assay was developed for enzymatic assay of plant invertases. In this assay, ADP produced from phosphorylation of glucose and fructose (hydrolysis products of invertases) is coupled to oxidation of NADH by the enzymes pyruvate kinase and lactate dehydrogenase in presence of phosphoenolpyruvate and NADH. This method was compared with the glucose-6-phosphate dehydrogenase method by using protein preparations derived from plant materials of three different species. Statistical analysis indicated that the alternative assay was similar in accuracy to the glucose-6-phosphate dehydrogenase method, with an advantage of reducing the cost from $0.85 to $0.35 per assay.
Paul W. Wilson, David H. Picha, and John M. Aselage
Changes in fructose, sucrose, and glucose were investigated in cured roots of `Beauregard', `Jewel' and `Travis' sweet potatoes stored at 15°C and 1.5°C for 8 wk. Samples of 6 roots each in triplicate were analyzed at 2 wk intervals. At each interval, samples were also heated for 5, 10, 20 or 40 min. at 100°C to determine changes in rate of maltose conversion. Roots stored at 15°C displayed gradual or no increase in sugars over the 8 wk. Roots stored at 1.5°C increased more rapidly in sugars, especially fructose, over the same time. `Jewel' had the greatest increase in the sugars when stored at 1.5°C. There was no consistent pattern of maltose conversion in roots stored at 15°C over the 8 wk storage time. Roots stored at 1.5°C displayed a reduction in ability to convert starch to maltose upon heating. Less maltose was produced with increasing time of storag at 1.5°C. `Beauregard' and `Jewel' changed the most, while `Travis' changed only slightly.
Yuehe Huang, David H. Picha, and Anthony W. Kilili
`Beauregard' sweetpotato (Ipomoea batatas L. Lam) roots were maintained under different controlled atmospheres ranging from 0% to 21% O2 at 22 °C in two separate trials for 14 days to study changes in activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH). Trial I showed no difference in activities of PDC and ADH between 0% and 1% O2, or among 2%, 5%, and 21% O2. Both PDC and ADH activities were significantly higher at 0% and 1% O2 compared to the 2%, 5%, and 21% O2 atmospheres. In trial II, both enzyme activities were lower at 1.5% O2 than at 0% O2, but higher than at 10% and 21% O2 atmospheres. The combined data of the two trials showed a very strong correlation between PDC and ADH activities (R 2 = 0.86). In addition, a strong correlation existed between PDC activity and acetaldehyde concentration (R 2 = 0.95). The maximal activities were at pH 6.5 for PDC and at pH 8.5 for ADH in the direction of acetaldehyde-to-ethanol. The results suggest that 1.5% O2 is the critical point for the transition from aerobic to anaerobic metabolism in CA storage of sweetpotato roots, and PDC is the key enzyme in alcoholic fermentation.
Don R. La Bonte, David H. Picha, and Hester A. Johnson
The quantity and pattern of carbohydrate-related changes during storage root development differed among six sweetpotato cultivars [Ipomoea batatas (L.) Poir. `Beauregard', `Heart-o-Gold', `Jewel', `Rojo Blanco', `Travis', and `White Star']. Measurements were taken for individual sugars, total sugars, alcohol-insoluble solids (AIS, crude starch), and dry weight (DW) at 2-week intervals from 7 to 19 weeks after transplanting (WAT) in two separate years. Sucrose was the major sugar during all stages of development, representing at least 68% of total sugars across all cultivars and dates. Pairwise comparisons showed `Heart-o-Gold' had the highest sucrose content among the cultivars. Sucrose content increased by 56% for `Heart-o-Gold' over the 12 weeks of assay, ranking first among the cultivars at 17 and 19 WAT and possessing 27% more sucrose than the next highest ranking cultivar, `Jewel', at 19 WAT. Fructose content profiles varied among and within cultivars. `Beauregard' showed a consistent increase in fructose throughout development while `Whitestar' showed a consistent decrease. The other cultivars were inconsistent in their fructose content profiles. Glucose content profiles were similar to those for fructose changes during development. The relationship between monosaccharides was fructose = 0.7207 × glucose + 0.0241. Cultivars with the highest fructose and glucose content could be selected by breeders after 13 WAT. Early clonal selection for high sucrose and total sugars is less promising because substantive changes in clonal rank occurred for sucrose and total sugars after 15 WAT. Cultivars ranking the highest in total sugars had either more monosaccharides to compensate for a lower sucrose content or more sucrose to compensate for a lower monosaccharide content. The relationship between DW and AIS was similar (AIS = 0.00089 × DW), and DW and AIS increased with time for most cultivars. Cultivars with high DW and AIS can be selected early during storage root development.