Sensory quality is important in assessing cultivars for fresh consumption as well as for the processing industry. Important quality attributes for fresh consumption were found to be color, taste, flavor, and texture attributes. Sensory properties of many tropical fruits with special emphasis on flavor notes and flavor compounds present therein have been described by Bauer (2000).
Flavor and odor of processed foods are among the most im- portant quality attributes, and while instrumental methods of evaluating them exist, subjective or human evaluation tech- niques are often more appropriate and more sensitive. There
Table 3.4. Major Flavor Constituents of Yellow Passion Fruit
Group Name of Compound (s)
Aldehydes 2- and 3-Methylbutanal, (E)-2-hexenal, benzaldehyde
Alcohols 1-Butanol, 2- and 3-methyl-1-butanol, 1-hexanol, (E)-3-hexen-1-ol, (Z)-3-hexen-1-ol, 1-octanol, 4-terpineol, nerol, 3-mercaptohexanol, geraniol, benzyl alcohol
Esters Ethyl butanoate, ethyl acetate, ethyl hexanoate, hexyl acetate, (E)-3-hexenyl acetate, hexyl butanoate, ethyl octanoate, (E)-3-hexenyl butanoate, ethyl 3-hydroxybutanoate, hexyl hexanoate,
(Z)-3-hexenyl hexanoate, diethyl succinate, ethyl 3-hydroxyhexanoate,␣-terpineol, benzyl acetate, hexyl octanoate, benzyl butanoate, benzyl hexanoate, ethyl cinnamate
Lactones 2-Butanone, cyclopentanone, 7,8-dihydro--ionone,-ionone,␥-decalactone
Hydrocarbons/terpenes Myrcene, limonene,␥-terpinene,trans--ocimene, 3-hydroxy-2-butanone, terpinolene, (E)-4,8-dimethyl-1,3,7-nonatriene
Others trans-Linalool oxide, linalool, hexadecanoic acid Source:Sidhu and Kabir 2010 (Adapted from Werkhoff et al. 1998).
are basically two types of subjective evaluation that may be carried out: consumer acceptance (preference) and panel difference methods. Consumer acceptance tests are utilized to evaluate new products, changes in manufacturing proce- dures, reformulations or line extensions of existing products, or for routine quality checking on the manufactured product vs. those of competitors. This type of testing requires a large number of consumers representing a good cross-section of the population.
In the panel difference method, a small group of individuals is trained to act like an instrument in describing attributes of processed products. Panelists might be screened by their ability to detect the four senses of taste: sour, sweet, bitter, salty, and their individual threshold levels for specific flavor or odor compounds. The particular method of flavor or odor evaluation depends on the product and its characteristics, the target market and the flavor or odor components of interest.
A number of product difference test exist, including paired comparison, triangle, dilution, ranking, numerical scoring, descriptive, and flavor or odor difference methods.
The main components of the overall sensation of flavor are taste and aroma (Salunkhe et al. 1991). Although taste and aroma are well integrated in their contribution to the overall flavor, aroma is often considered to play a dominant role in flavor (Goff and Klee 2006, Voilley and Souchon 2006, Baldwin 2008). The receptors on the tongue are responsible of perceiving flavors, while aroma generally contributes to total flavor.
Bursac et al. (2007) reported the sensory characteristics of fresh fruit and its purees in two strawberry cultivars, “Maya”
and ”Queen Elisa,” conventionally and organically grown in Croatia. Conducted sensory evaluation indicated that there were slightly expressed some differences in sensory attributes observed by panelists between two different cultivars and two types of cultivation, but they did not show significant differ- ences in any sensory attribute when dealing with two different strawberry cultivars or two types of cultivation (Bursac et al.
2007).
Baldwin et al. (1998) and Krumbein and Auerswald (1998) reported that the volatile compounds clearly influence odor and flavor perception in tomatoes, and although over 400 aroma substances have been identified in tomato fruit (Petro- Turza 1987), only about 30 of them are considered to be important for flavor based on their odor thresholds (Buttery and Ling 1993). Another critical component for consumer’s perception of tomato fruit quality is texture (Causse et al.
2002, Serrano-Megias and Lopez-Nicolas 2006). Fruit tex- ture is the result of many sensory attributes such as firmness, mealiness, meltiness, juiciness, and crispness (Harker et al.
1997, Redgwell and Fischer 2002, Szczesniak 2002).
The sensory quality of fruit has become a major crite- rion in making the purchasing decision by consumers. The sensory quality of fruit involves a range of attributes such as sweetness, acidity, aroma, firmness, and color. In the last decades, consumers have often complained about the poor
eating quality of fruit put into the market and flavor has now become a major criterion in making the purchasing decision.
The sensory quality of fruit depends on many factors, includ- ing variety, culture conditions, picking date, and postharvest handling and storage methods. However, among these fac- tors, the genotype is probably the most critical.
Preharvest Conditions
The rate of maturity stage at harvest is one of the most im- portant factors (after genotype) influencing flavor quality of fruits. Synthesis of nonvolatile and volatile compounds in- fluencing fruit flavor increases with maturation and ripening.
However, harvesting fruits before they reach optimal maturity is a common commercial practice because of the higher prices when the supply is low at the beginning of the harvest season of each kind and cultivar of fruits. Minimum maturity indices are often not enforced by the regulatory authorities. Another reason for harvesting climacteric fruits before their optimal maturity stage based on flavor is to assure sufficient firmness to withstand handling procedures and to maximize their stor- age potential. However, Fellman et al. (2003) showed that when apples are harvested at the early preclimacteric stage and kept in either air or controlled atmospheres (CA) for various durations before marketing, they never reach good eating quality.
The flavor of any fruit is a combination of sensory re- sponses in the nose and mouth to odor and taste. A large number of constituents such as acids, sugars, volatiles, and many other miscellaneous compounds individually or syn- ergistically elicit sensory responses that are recognized in total as a flavor of that particular fruit. Accumulation of these compounds during growth, development, as well as during ripening and/or senescence is largely influenced by the genetic, preharvest, harvesting, and postharvest factors (Mattheis and Fellman 1999). Apple is extensively cultivated in many areas around the world. Echeverria et al. (2004a) have studied the effect of harvest date and cold storage on the volatile compounds of “Fuji” apples. They obtained the highest amount of aroma compounds after 5-month storage and one day of ripening at 20◦C for the early harvested fruit. Ethyl 2-methylbutanoate, 2-methylbutyl acetate, and hexyl acetate were the major aroma compounds responsi- ble for the characteristic aroma of “Fuji” apples. According to them, storage conditions and season had a significant ef- fect on the aroma volatile compounds of apples. The effect of optimum harvest time on the sweetness, sourness, and aroma compounds during CA storage of red delicious ap- ples has been investigated by Fellman et al. (2003). With the advance of harvest maturity, the time required to regener- ate aroma volatiles to an optimum level after removal from CA storage decreased significantly. Lopez et al. (2007) have reported that the soluble solids, TA, background color, and emission of hexyl 2-methylbutanoate, hexyl hexanoate, hexyl propanoate, butyl 2-methylbutanoate, 2-methylbutyl acetate,
and butyl propanoate contents positively influenced the ac- ceptability of “Pink Lady” apples during 25 days of cold storage. In another study on the same variety of apple, Vil- latoro et al. (2008) had observed low production of aroma volatiles in the early harvested fruit, but the volatiles gradu- ally increased as the ripeness approached.
Ong et al. (2006) have evaluated the chemical composi- tion (i.e., TA, moisture content, crude fiber, color, pH, soluble solids, sugars, organic acids) and flavor changes during the 5-day ripening of jackfruit (Artocarpus heterophyllusL.). A high amount of malic acid was found in unripe fruit, but the ripe fruit contained a high amount of citric acid at the optimum day (5th day) of ripening. Using GC and GC-MS, they identified a total of 23 volatile compounds in the ripened jackfruit. Mango fruits at different maturities (61–115 days past flowering) have recently been studied for aroma volatile using e-nose and gas chromatography as well as for solu- ble solids and acids (Lebrun et al. 2008). They found, both the e-nose and GC were able to separate mango fruit from different harvest maturities. Soluble solids and acids data in- dicated that later-harvested maturities gave sweeter fruit with a different volatile profile than the earlier-harvested mango fruits.
Postharvest Conditions
Medicott et al. (1990) studied the changes in mango flavor with respect to the storage temperature and demonstrated that the mangoes stored at relatively low temperature exhibited higher flavor scores. Ripe fruit characteristics and flavor in- tensity are also reported to increase with storage (MacRae et al. 1989). Abbasi et al. (2009) attributed the change in the mango taste to storage time and reported that taste score of mango increased from 3.54 to 8.42 after four weeks of storage. Inhibition of volatile biosynthesis is caused mainly by limited precursors/substrate supply to the related enzymes rather than by enzyme degradation or inactivation during CA storage of pears and apples (Lara et al. 2003, Echeverria et al.
2004b, Lara et al. 2006). Free FA and particularly oleic and linoleic acids have demonstrated the best relationship with aroma volatiles biosynthesis in preclimacteric and climac- teric apples during CA storage (Song and Bangerth 2003).
They concluded that de novo biosynthesis of FA rather than their release from membranes or storage pools represents the limiting step in the volatile aroma production of apple fruits.
The effect of methyl jasmonate on the production of aroma volatiles in apple fruit may be mediated by ethylene (Kondo et al. 2005). Calcium application has been shown to improve the aroma quality and other key standard quality parameters after mid-term storage of “Golden Reinders” fruit and this offers a simple but economical alternative to CA storage of this apple cultivar (Ortiz et al. 2010).
Fallico et al. (1996) have shown that storage tempera- ture affects the sensory-influencing qualities of blood orange juice. In particular, vinylphenol concentrations (the malodor-
ous substances that arise from free hydroxycinnamic acid de- carboxylation) in juices stored at 4◦C and at 25◦C for over 4 months exceeded the odor threshold value. Moshonas and Shaw (1989) found that the hedonic flavor of commercial or- ange juice decreased most rapidly during the first week or two of storage. Higher storage temperatures produced the greatest decrease in flavor scores. Obenland et al. (2008) have char- acterized the aroma-active volatiles of navel oranges using GC-olfactometry as well as the soluble solids concentration (SSC), TA, ethanol concentration, percent juice recovery, and sensory quality (freshness, tartness, sweetness, and like- ability). Freshness and likeability decreased as a result of storage only in the packed fruits. They concluded that com- mercial packing and storage of navel oranges alters the aroma volatiles and reduces their flavor quality.
Carbon dioxide-stored (at 5◦C) strawberry fruits (cv. Dia- mante) had a better shelf life (11 days) than those stored in air (9 days) when evaluated for flavor components such as sugars, organic acids, aroma compounds, and fermenta- tive metabolites (Pelayo et al. 2003). Bagging of peach (cv.
Hakuho) fruits (15 days before harvest) has been shown to improve the fruit skin color through the reduction of chloro- phyll content and increased fruit flavor through the increase in aroma volatile content (Jia et al. 2005). Effect of hyperbaric and CA storage and prestorage treatment with UV radiations on the volatiles of peach fruit have been studied by Yang et al. (2009). About 65 volatiles have been indentified in fresh peach fruit and after 4 weeks of storage. The concen- tration of total volatiles and esters had increased by 32.5- and 36.5-fold during storage, respectively. The effect of CA stor- age on the volatile composition of “Hayward” kiwifruit has been investigated by Burdon et al. (2005). They suggested that the alcohol metabolism contributed significantly to the ripe fruit volatile profile of kiwifruits, especially the ester production.
Thirty-eight volatile compounds have been reported in
“Bartlett” pear fruits treated with 2,4-dichlorophenoxy- propionic acid with esters being the most prevalent com- pounds and butyl, ethyl, and hexyl acetate were produced in the largest amounts (Kondo et al. 2006). In case of black- currants (Ribes nigrum L. cv. “Titania”) stored in air and under CA, 53 volatile compounds have been reported using GC-MS techniques (Harb et al. 2008). The air-stored fruits synthesized more of total terpene volatiles, and the nonter- pene compounds, mainly esters and alcohols, also increased under these storage conditions. In blackcurrants juice, ter- penes together with esters and alcohols are the major groups of aroma compounds. Hanekom et al. (2010) have investi- gated the effect of sulfur dioxide fumigation, modified atmo- sphere packaging (MAP), and CA packaging on the changes in volatiles and sensory characteristics of litchi fruit. Cit- ronellol and geraniol are responsible for the fruity, floral, rose, and citrus aroma in “Mauritius” litchi fruit. The reten- tion of these aroma volatiles in litchi fruit during storage followed the trend: MAP ⬎ CA ⬎SO2 ⬎SO2–HCl dip.
The MAP packed litchi fruit showed no decay and reduced pericarp browning with acceptable marketability.
Flavor and Packaging Interactions
In commercial products, initial flavor has little meaning if that same flavor is not present when the product is consumed. The flavor changes that occur between production and consump- tion are of enormous interest to the food and flavor industry.
Many factors have to be considered. Unfortunately, many flavor-active components are also highly chemically reactive and will react with each other, other product components, or with the packaging they come in contact with. Moshonas and Shaw (1989) reported that the flavor score decreased during 6-week storage of commercial orange juice due to increased levels of ethyl acetate, which they speculated may have come from the laminated multilayered package liner.
Imai et al. (1990) monitored the sorption of d-limonene, neral, and geraial from orange juice into three sealant films during 24-day contact at 22◦C. They found the copolyester had less sorption of the organic volatiles than ethylene vinyl copolymer or commercial low density polyethylene. Konczal et al. (1992) carried out a similar study with apple juice; how- ever, they used dynamic head space to determine sorption.
Sorption of the apple juice volatiles was most significant for the low density polyethylene than with the two developmen- tal polymers.
Sadler et al. (1995) discussed the interaction of orange juice with various packaging polymers. They found that d-limonene absorption increased microbial proliferation and accelerated vitamin C degradation. They were able to calcu- late the time required for identifiable flavor loss using diffu- sion, solubility, and permeation data. Two inexpensive meth- ods for evaluating the interaction between volatile organic compounds and packaging polymers were also presented.
Manurakchinakorn et al. (2004) reported that fresh-cut fruits with MAP treatment obtained the highest sensory scores, compared with other treatments, throughout the entire period of storage. Fresh-cut mangosteens (Garcinia man- gostana L.) stored in MAP resulted in the best overall re- tention of ascorbic acid, antioxidant capacity, and sensory quality.