Progress 10/01/02 to 09/30/07
Outputs
Apple is a complex material in that it changes structure classification from a non-porous material at the beginning of drying to a porous material during the drying process. The results for the prediction of apple samples indicate that two mechanisms may govern the moisture transfer during drying, where a diffusion mechanism may dominate the transfer at the beginning when the material is non-porous and a phase-change mechanism towards the latter stages of drying when the material is porous. In the United States, over 13 million tons of apples are used to process juice and cider. Based on a 75 percent extraction efficiency, about 810 million pounds of apple pomace is generated as the primary waste product from juicing alone. Disposal of this high volume waste product has become a crucial issue in apple manufacturing plants. Apple pomace has a moisture content of about 70 percent, therefore the wet pomace spoils quickly. The pomace is often produced into cattle feed,
which must be fed to cattle immediately before it spoils. Therefore the pomace must be dried into a shelf-stable product prior to disposal. Other more elaborate methods have been introduced to utilize this waste product into useful by-products, including production of natural gas, production of citric acid, conversion to charcoal, isolation of pectins, and fiber extracts. Due to the expense of production of these by-products, cattle feed is still the most common means of disposal. We have shown that dried apple pomace has tremendous potential as a press aid to berry juice extraction, and juice producers and extraction equipment manufactures have expressed strong interest in utilizing dried apple pomace as an alternative press aid. Moreover, interests have grown to produce other value-added products from dried apple pomace and peel, such as ingredient powders. Apple pomace, which is the largest waste of apple juice production, has been investigated as an alternative press aid. Results
have shown that berry juice yields using dry apple pomace press aid were similar to juice yields produced with standard press aids. Triangle difference tests showed that there were differences between the berry juices pressed with conventional press aid to the berry juices pressed with apple pomace press aid, and paired comparison preference tests showed that the berry juices pressed with apple pomace were preferred. Flavor analysis using gas chromatography/olfactometry indicated possible off-flavors being extracted from rice hulls, such as indole and 4-vinylguaical which are characterized as resinous and mothball aromas, and from paper, such as (Z)-2-octenal and 2-nonenal which are characterized as cardboard aromas, into the berry juices. Concerning berry pomace disposal, use of apple pomace as a press aid has an advantage over rice hulls and paper in that it can be fed to cattle. Therefore, apple pomace press aids are more environmentally friendly than other traditional press
aids.
Impacts
Fresh fruits have high moisture contents, so dehydration of fruits is an energy intensive process. Food production costs in New York State can be as high as 13 cents per kilowatt-hour; therefore, the importance of an optimized drying process is apparent. This work provided a better understanding of the mechanism(s) that control the drying process for apples, thus more energy efficient drying processes can be developed as well as higher quality dehydrated products.
Publications
- Srikiatden, J., and Roberts, J.S. 2005. Moisture transfer in apple during convective hot air and isothermal drying. International Journal of Food Properties (in press).
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Progress 01/01/04 to 12/31/04
Outputs
Grape pomace, which consists of grape skins, seeds, and stem, is a high volume waste product from juice and wine production. This pomace has tremendous potential of being a source of value-added products, such as grape seed oil, but currently the pomace is used as animal feed or mulch. Cold mechanical pressing of dried grape seeds offers an environmentally friendly process to extract oil without using chemicals. This press requires that the seeds have a moisture content below 10 g water/100 g dry solids (10 percent dry basis). Wet seeds from pomace have a moisture content of 95 g water/100g dry solids (or 49 percent wet basis), and therefore the seeds must be dried. We have conducted dehydration kinetic studies of grape seeds at 40, 50 and 60 degree Celsius. The grape seeds were of variety Riesling, Concord, and Cabernet Franc, and were separated from the pomace using a Bertocci separator. To conduct these dehydration studies on materials considered particulates, a
basket was constructed with a screen on the bottom to both allow solid materials to rest and allow air flow to pass through. This basket was suspend from an analytical balance into a convective oven. An air flow chamber, 10 cm in diameter, was constructed from polycarbonate and placed in the oven. With the fan in the oven drawing air downward toward the center floor of the oven, the reduced diameter of the chamber created air flow with velocity of 2 m/s. Equilibrium moisture content is a critical parameter in dehydration studies, and this can be determined by either having the sample dry for an extremely long time until no measurable moisture loss is observed or by a more precise method of conditioning a smaller sample at a given temperature and relative humidity environment. The latter method is known as a moisture sorption isotherm technique, and equilibrium moisture content was determined at 50 degree Celsius and 7 percent relative humidity. The relative humidity environment was
established from a saturated lithium bromide salt solution. After equilibration was reached from drying and conditioning, the samples were removed and placed in a vacuum oven to determine initial and final moisture contents based on the weights taken before and after drying and conditioning and the weight of the dry solids after vacuum oven treatment. The equilibrium moisture content determined from extended drying times were similar to the equilibrium moisture content determine from moisture sorption isotherm.
Impacts
Apple and grape pomace are high volume waste products generated from cider, grape and wine manufacturing facilities. Work conducted in this laboratory as well as in this department has shown that value-added products can be produced from these waste materials; however, these materials need to be dried in order prevent spoilage or allow further processing to take place, such as dry seeds needed for seed oil extraction. Our work on the drying kinetics will allow for more efficient drying processes to be developed.
Publications
- Roberts, J.S., Gentry, T.S., and Bates, A. W. 2004. Utilization of dried apple pomace as a press aid to improve the quality of berry juices. Journal of Food Science, 69(4): S181-190.
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Progress 01/01/03 to 12/31/03
Outputs
Common press aids used in berry juice extraction include rice hulls and paper; however, off-flavors can be imparted into the juice from these press aids. Dried apple pomace has been shown to produce similar juice yields but with significantly better flavor. From physicochemical analysis, the berry juices pressed with apple pomace resulted in higher soluble solids and higher sugar to acid ratio than the juice pressed with standard press aid. In this next phase of the project, dried apple pomace was tested to determine whether the press aid was contributing soluble solids and organic acids to the berry juices as a result of heated water, maceration enzyme, or juice extraction pressure. Apple pomace press aid (1 percent) was mixed with distilled water (100 ml) heated to 49 oC with and without maceration enzyme preparation containing pectinase, hemicellulase, and cellulase (0.1 ml /kg water). Since press aids are added just prior to the fruit slurry entering the press,
the contact time of the press aid in the heated and enzyme treated slurry is between 15 and 30 minutes. Only when very large batches of fruit slurry exceed the throughput capacity of the press will a press aid be in contact with the heated slurry for an extended period of time, which can be as much as 45 minutes. This would be the worst case scenario since the berry slurry could begin to loss quality from the extended heat and enzyme treatment. Therefore, the solution was monitored at 0, 15, 30 and 45 minutes for soluble solids and titratable acidity. Since malic acid is the predominant organic acid in apples, the titratable acidity was based on percent malic acid (g/100 ml). Each experiment was repeated six times. The effect of pressure used during juice extraction on the press aid was also tested. The results show soluble solids increased significantly with soak time in each of the solutions. The enzyme treatment did not have an effect on the apple pomace with respect to soluble
solids. The results of the malic acid present in solutions varied. There was no increase in malic acid in the 1 percent pomace press aid without enzyme as well as in the 1 percent pomace with enzyme solution up to 30 minutes of soak time, with only a slight increase at 45 minutes from 0.01 to 0.02 g acid/100 mL. These results showed that though the soluble solids and percent malic acid increased with soak time, the increase for the 1 percent pomace press samples were less than 5% of the berry juice soluble solids and acid. In the berry juice extraction experiments for which the physicochemical properties were measured, the press aids were only in the slurry for less than 15 minutes throughout the entire process. The soluble solids and acid at 15 minutes were significantly less than the soluble solids and acid at 45 minutes. Also, the extraction pressure did not have a significant effect on the extraction of soluble solids and acids form the press aid. Therefore, the most significant
processing factor effecting soluble solid and acid extraction from the apple pomace press aid is the soak time in heated water.
Impacts
Juice processors and extraction equipment manufacturers are interested in the use of dried apple pomace as a press aid, though several have inquired about the leaching potential of dried apple pomace press aid into the berry juice. This study has shown that apple pomace can be used as a press aid to produce an improved berry juice over conventional press aid without leaching of sugars or acids. Results of this project will also be presented to the wine industry as a better method for grape juice extraction.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
The use of small fruit (berries) has shown large growth in the juice industry, particularly in blended juice products. With raw berries being expensive, high yields are important. Therefore, screw presses, which require press aids to work properly, are frequently used during juice extraction. Common press aids include rice hulls and paper; however, off-flavors can be imparted into the juice from these press aids. Dried apple pomace has already been shown to produce juice yields to juice produced with standard press aids. Previous sensory tests indicated differences between the press aids. The berry juice pressed with apple pomace was preferred to the control. Raspberry and blueberry juices were reported as sweeter with a fuller flavor and a fresh taste. Juices processed with either rice hulls or paper were describes as bitter, stringent and having a woody flavor. There is a definite need to identify the flavor compounds being extracted form the press aids during juice
extraction. Therefore, one objective of this study was to analyze the effects of press aids on berry juice quality using gas chromatography/olfactometry (GC/O) and evaluate the potential of apple pomace as an alternative press aid. Strawberries, raspberries, and blueberries were used in this extraction study. The berry samples (150 g) were mashed and heated to 50 C and held for one hour. 100 g samples were then pressed using the different press aids at 1 percent concentrations. A cell attached to a Carver Press was used to apply the extraction pressure (1,500 psi). From the water or juice collected, pH, total acids, and Brix were measured and flavor compounds were analyzed. For the flavor analysis, a 20 mL sample was taken and sonicated at 20 C for 10 min with 10 mL of Freon. The sample was then separated. The lower phase (freon) was collected and the upper phase was rinsed with an additional 10mL of freon and separated. This was repeated for a third time. The collected phase (30 mL)
was then concentrated to 1 mL using a rotovap. Finally, a 1 mL sample was injected onto a 30 m x 0.32 mm 0.D. DB-5 column having a sniff port attached. The column was held at 35 C for 3 mins and ramped 6 C/min upto 250 C. The column was held at the final temperature for 3 minutes. GC/O analysis indicated rice hulls and paper imparted woody and earthy off-flavors, while the juices extracted with apple pomace retained their characteristic flavor profiles. Apple peel have also shown tremendous potential as a press aid in berry juicing. The advantage of using apple peel over apple pomace is that the drying requirement is significantly less, thus the energy requirement is less. The drying kinetics of apple peel under convective drying conditions was initiated. A sample basket constructed to simulate a tray in a cabinet dryer was used to suspend peel samples from an analytical balance, which is place on top of a lab-scale convective oven. A polycarbonate cylindrical chamber is placed within
the oven and over a fan at the bottom of the oven to create the necessary convective air flow. Drying curves of apple peel have been obtained at 50 and 70 C.
Impacts
The use of apple pomace and apple peel as an alternative press aid is promising. Many large and small juice processors are extremely interested in knowing both the impact on the juice flavor and the energy requirements needed to develop apple pomace and apple peel press aids. This quantication of flavors extracted from press aids shows the advantage apple pomace has over conventional press aids, and the drying kinetics of pomace and peel allows for determining the energy requirements needed to dry the apple pomace and peel.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
Apple pomace is the principal solid waste from apple juicing. It is rich in carbohydrates, low in protein, and has various uses. The major utilization of this waste product are as cattle feed and as a soil conditioner. Recent studies in our lab have shown tremendous potential for the use of dried apple pomace is as a press aid in berry and grape juicing. Therefore, the drying kinetics and moisture sorption isotherm of wet and dry pomace will be beneficial to evaluate the drying process and storage. The red delicious apple pomace was a waste product of a previous pressing. It was dried, milled, sifted, and stored in a sealed container. The drying was done in a cabinet dryer, because of its ability to handle small batches, for two hours at 70 C. The dried pomace was put through a hammermill (Buffalo Hammermil Corporation, Model W-4 SS) to attain the desired particle size. At 15 C, a sample of red delicious apple pomace was weighed and placed into a plastic dish in the
water activity meter to determine the initial water activity. After equilibration was reached, the sample was removed and placed in a vacuum oven to determine initial moisture content. Subsequent pomace samples were placed into the water activity meter where the sample chamber was conditioned to 43%, 33%, 22%, 11%, and 7% relative humidity to obtain a desorption isotherm at 25 C. The samples were also conditioned from low humidity to high humidity to obtain a re-absorption isotherm. The same procedure was used to evaluate the pomace at 35 C and 45 C. To evaluate drying kinetic of apple pomace, a basket was constructed with a screen on the bottom to both allow solid materials to rest and allow air flow to pass through. This basket was suspend from an analytical balance into a convective oven. An air flow chamber, 10 cm in diameter, was constructed from polycarbonate and placed in the oven. With the fan in the oven drawing air downward toward the center floor of the oven, the reduced
diameter of the chamber created air flow with velocity of 2 m/s. Wet pomace (78% g water/g sample) was placed in the basket and dried at 70 C until equilibrium was observed.
Impacts
Once drying kinetics is completed, a drying model can be developed to predict moisture loss behavior under various drying conditions. Thus, the preparation of apple pomace to a press aid will be more predictable and easier to accomplish to those wanting to produce this value-added waste product.
Publications
- No publications reported this period
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Progress 01/01/00 to 12/31/00
Outputs
The status of this project is that the isothermal apparatus, which includes a microwave oven with continuous variable power control and a forced hot air convective blower, has been set-up and running. The final apparatus set up is the feedback temperature controller, which requires some program modification. The materials for the convective hot air system have been acquired, and after the isothermal system is finished the convective system will be put together. A data acquisition system to read and record time-temperature data has been developed, so up to ten thermocouples can be used in the convective system. An image grabber and software was also acquired to monitor sample shrinkage during drying, and this information will be used to quantify shrinkage during moisture loss and determine its effect on moisture transfer. Cherries were osmotically dried in a 68 degrees Brix solution and then sun dried. A greenhouse was shown to reach 60 degrees Celsius, which is a
suitable temperature to dry fruits in reducing carmelization of the sugars in the fruit. With the addition of a blower in the greenhouse to make the room have convective air movement and aid in moisture removal, the potential for a low energy alternative to conventional drying is shown.
Impacts
(N/A)
Publications
- No publications reported this period
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