Relationship Between SSC/TA Ratio and Acceptability of Navel Orange

Transcription

1 PROJECT CONCLUDED: FINAL REPORT Relationship Between SSC/TA Ratio and Acceptability of Navel Orange Mary Lu Arpaia Botany and Plant Sciences UC/Riverside and Kearney Ag Center, Parlier David Obenland USDA/ARS, Parlier Overview of Year 4: This was the final year of a 4-year project conducted to evaluate the relationship between soluble solids content/titratable acidity (SSC/TA) and other potential indicators of flavor with navel orange acceptability. During the season, we addressed two main questions: (1) Were our previous results valid for consumers rather than just the experienced panelists at the Kearney Agricultural Center? and (2) If the maturity standard were to be changed, how much of an increase in SSC/TA would be necessary for a consumer to tell a difference? To accomplish this, tests were conducted in collaboration with Dr. Michael O Mahoney (UC/ Davis) where fruit from packinghouses were transported to Davis and evaluated by consumer testing. The same fruit was also evaluated in a similar manner at the Kearney Agricultural Center (KAC) in order to determine whether or not the results from the Kearney panel gave results similar to those from a true consumer panel. Testing was continuously performed over the early part of the season from mid-october to the first week of January. The results from both UC/Davis and KAC were quite similar, indicating that results from KAC approximate those Table 1. Determination of the minimum difference in SSC/TA needed for a sensory panelist to detect that a difference exists. When a difference was correctly noted a sufficient number of times to give statistical significance, the difference was said to be detectable. Data from the KAC panel. Min. SSC/TA Diff. Max. SSC/TA Diff. Correct Evaluations Detectable? /32 No /16 Yes /32 No /32 No /28 No /136 Yes /28 Yes /60 Yes /52 No /40 Yes /56 Yes /30 Yes /28 Yes Figure 1. Comparison of SSC/TA versus BrimA for prediction of orange acceptability (liking). BrimA = SSC - (3*TA). from an actual consumer panel and giving additional validity to work from the prior 3 years. In table 1 is shown results obtained from presenting KAC panelists with pieces of fruit with differing SSC/TA ratios and determining if they could detect a difference. For differences in SSC/TA less than 2.0, the panelists were not able to consistently detect a difference. Experimentation at UC/Davis came to the same result. Purchase intent testing at UC/ Davis indicated that 75% of panelists said that they would purchase oranges with a higher ratio ( ) over ones with a lower ratio ( ). In describing the reasons for a purchase decision for ratios from 8 10, panelists cited juiciness and the right amount of sourness or sweetness as being positive factors, while those that would not purchase were mostly concerned with the fruit being too sour. At ratios of 11 or higher, the predominant reasons for saying they would purchase the fruit were the fruit having a proper amount of sweetness, juiciness and flavor balance, with lack of flavor being the main reason for deciding not to purchase. In another experiment, panelists ranked fruit with different ratios for likeability (Figure 1). Although there was an upward trend of increasing likeability with increasing ratio, there was a great amount of variation in the data. Of greater interest in this data was the finding that BrimA (SSC (3*TA) was much more closely related (higher R 2 ) to likeability than SSC/TA. This supported work from the earlier years of this project. Overview of Entire Project: Primary Project (SSC/TA and Acceptability) One of the findings of this project was that SSC/TA may not be the best overall predictor of acceptability. Our results, combining three seasons of data, indicated that BrimA and external color (subjective evaluation with color chart) were the best predictors, while SSC/TA was slightly inferior (Table 2). Color, while easy to measure, would likely not be a good substitute for SSC/TA due to the strong influence of climate on its development. BrimA, like SSC/TA, has SSC and TA as its major components but is calculated by subtracting TA times a constant from SSC rather than dividing (BrimA = SSC 3*TA). As was previously mentioned, sensory experi-

2 mentation at UC/Davis done for this project also showed the superiority of BrimA over SSC/TA. Closer examination of our data, however, indicated that while BrimA is better than SSC/TA overall, there was only an advantage with low acid fruit (TA < 0.7) and not with higher acid fruit as occur early in the season. Unless there are instances of low acid fruit at this time in the season, use of BrimA instead of SSC/TA may hold no advantage. In addition to standard quality parameters such as SSC and TA, volatile compounds are very important components of flavor. Part of the reason that SSC/TA does not accurately predict flavor in many instances is because the presence of these components is not taken into account. In the third year of the project, aroma-active compounds were quantified at various points during the season to identify volatiles that are important to flavor development during fruit maturation. Nineteen compounds were identified as having active aromas and potentially contributing to flavor, with six being significantly correlated with the hedonic score (Table 3). This in- creased knowledge of volatile flavor components could eventually lead to a use of volatile profile as an additional tool to help ensure that fruit are adequately mature. Evaluation of the data from the first three seasons of testing at KAC indicated that the panelists disliked fruit at a SSC/ TA ratio of 8:1. The plots shown in Figure 2 were used to calculate predicted values of the hedonic score and BrimA at each SSC/TA level (Table 4). These relationships were found to be the same across years, different locations and different navel strains. It can be seen in Table 4 that a SSC/TA of 8:1 corresponds to a hedonic score of 4.4, which falls between 4 (dislike slightly) and 5 (neither like nor dislike). Increasing to 10 raises the hedonic score to 5.2, indicating that the panelists were fairly neutral about the fruit. It was not until a SSC/TA of 13 that the hedonic score reached 6.0 (slightly like). The data strongly suggests that the maturity standard needs to be raised above 8:1, preferably to at least 10:1. This fits in with the work done at KAC and UC Davis (described in Year 4 overview) that found that an increase of at least 2 points is needed for consumers to be able to perceive a difference and also agrees with previous recommendations (Ivans and Feree, 1987; Pehrson and Ivans, 1988). Table 2. Pearson s correlation coefficients between sensory data and measured quality attributes using three seasons of combined data. A higher value indicates a closer relationship. Color % Juice SSC TA SSC/TA BrimA Hedonic Score Sweetness Tartness Richness Color = external rating using a color chart; % Juice = weight of the juice as a percentage of the total weight of the fruit; SSC = soluble solids concentration; TA = titratable acidity expressed as percent citric acid; BrimA = SSC 3(TA). Hedonic score is a measure of likeability.

3 Table 3. Pearson correlation coefficients between aroma-active compounds and sensory attributes as determined from a series of five harvests throughout the first 4 months of the navel orange season. A star following a correlation coefficient indicates statistical significance (P? 0.05). A higher value indicates a closer relationship. Sensory Attribute Compound Aroma Descriptor Hedonic Sweetness Tartness Richness unknown 1 (U1) alcohol, sweet 0.87* 0.83* 0.83* 0.77 unknown 2 (U2) metallic 0.88* 0.89* 0.86* 0.79* pentanal (PEN) sour, pungent unknown 3 (U3) sour 0.89* 0.91* 0.83* 0.76 hexanal (HEX) grassy ethyl butanoate (EB) fruity 0.86* 0.87* 0.85* 0.78 heptanal (HEP) fatty ?-pinene (PIN) spicey octen-3-one (OCT)x mushroom unknown 4 (U4) fatty, lemony 0.87* 0.88* 0.91* 0.83*?-myrcene (MYR) fatty, musty ethyl hexanoate (EH) fruity 0.91* 0.92* 0.91* 0.85* octanal (OCT) fatty, lemony limonene (LIM) minty ?-terpinene (TER) citrus linalool (LIN) citrus unknown (U5) cereal, fatty (E)-2-nonenal (NON) fatty ethyl octanoate (EO) fruity, floral

4 Summary for Primary Project: Reasons to Raise to 10:1 (1) Fruit are disliked by consumers at 8:1, and raising to #10:1 will increase the acceptability of the fruit; (2) Results from both KAC and UC/Davis suggest that an increase in the SSC/TA ratio of at least two points is needed for a consumer to tell a difference; (3) Since the maturity standard is based on pooled samples, raising the standard to 10:1 would minimize the number of very low ratio fruit reaching the marketplace. Overview of Secondary Projects: Project 1 Comparison of W. Murcott and Tango: This work, done in collaboration with the Roose group at UC Riverside, consisted of evaluating both W. Murcott and Tango for external appearance, peelability and flavor, with the goal being to determine if any differences existed. Tests were conducted using five separate harvests with storage conditions of 0, 3 and 6 weeks. The conclusion from the work was that W. Murcott and Tango were very similar with 13 out of 15 tests showing no appearance differences, 10 out of 15 showing no flavor differences, and none of the tests indicating any differences in peelability. Project 2 Comparison of juicing and juice measurement methods: The purpose of this project was to compare both juicing methodologies and means of measuring SSC and TA to determine if the methods used by KAC (Hamilton Beach Press and digital refractometer) give different results than the methods used by industry (Boswell Press and hygrometer). This was needed to be able to better compare our overall findings to commercial conditions. The final results indicated that the Hamilton Beach Press gave a slightly lower SSC/TA ratio (9.49) than did the Boswell Press (9.79), while the digital refractometer gave an overall SSC/TA value (9.92) that was slightly higher than the hygrometer (9.74). The way the juicing is conducted and how SSC is measured can make a difference in the final SSC/TA reading, but in our comparisons the differences were fairly small. Of greater interest was the observation that SSC readings taken by hygrometer tend to be more variable than readings taken by other methods tested. Replacement of the hygrometer with a refractometer would be a beneficial step by the industry. Project 3 Influence of waxing and packline handling on fruit acceptability: Comparisons were made between different wax types (carnauba and shellac) and manufacturers, and no differences in the taste of the fruit after storage were found due to either of these two factors. Experiments were also conducted where fruit were taken from various points in the commercial packing process (bin, after washer, after waxer, packed box), stored, and then analyzed for both sensory qualities and volatile composition. These comparisons were useful in trying to separate the effects of the mechanical impacts of the packline from the waxing effect. Ethanol readings from the fruit indicated that the packline itself Table 4. Hedonic taste score obtained from a given SSC/TA ratio, the corresponding BrimA, and the average date over a three-year period that this SSC/TA ratio occurred on. SSC/TA Hedonic Score x BrimA x Average Date y September October November November December December January 11 x Hedonic taste scores and BrimA calculated from equations in Figure 2. y Three-year average. Figure 2. Relationshsips between SSC/TA or BrimA and hedonic score (acceptibility). Each data point represents an individual tasted fruit (over 2000 fruit were tasted). Three seasons of combined data. Hedonic score of 6 = slightly like. (even without waxing) had a physiological effect on the fruit. These differences did not translate into noticeable changes in taste, however, as the taste was not significantly different until after the waxing step. Both the packline and storage had a negative effect on taste. The changes in eating quality were found to be due to differences in flavor volatiles rather than changes in SSC or TA. This work was published in the journal Postharvest Biology and Technology (47: ).

5 NOTICE: The research results included in this publication are summary reports for the benefit of the Citrus Research Board and the growers it serves. They are not to be taken as recommendations from either the individual reporting or the agency doing the research. Some of the materials and methods mentioned are neither cleared nor registered for commercial use. The summaries were written by the project leaders identified. Both technical names and registered trademarks of materials are used at the discretion of the authors and do not constitute any endorsement or approval of the materials discussed. Questions on possible applications should be directed to the local University of California Extension Specialist, a licensed PCA, or the appropriate regulatory agency.