AN IMPROVED METHOD FOR MEASUREMENT OF PULP

Transcription

1 84 FLORIDA STATE HORTICULTURAL SOCIETY, 167 The moisture level of 1.% found optimum in these studies is in agreement with results from actual densification observations on a pilot plant scale. The optimum densification pressures ob served here are only about half those observed effective in pilot runs, however. In the pilot runs the foam-mat crystals are fed into the nip of nine-in. diameter heavy steel rolls turning about 16 rpm and removed by a doctor blade. The differences between pilot runs and laboratory runs with respect to pressure required are prob ably due to differences between a static system (as in the present study) and a dynamic sys tem, (as in the pilot plant studies). In the statis system, the sample is subjected to pressure over a relatively long time (5 sec) whereas in the dynamic system the pressure is only applied to the sample for a fraction of a sec. This probably accounts for the differences in required pressures in the two systems. The studies with the static system have shown that it is possible to use pressures which are too high for optimum densification, and this is in agreement with ob servations in the dynamic system. Thus, although the values are not directly comparable, the same principle appears applicable in both systems. A coincidental factor in this study was the suggestion of a prospective new form for a citrus product. During this study, several investigators began eating some of the formed discs and found that they were very tasty. The amount of solids equivalent to one ounce of juice was also found to compress nicely into a bite-sized disc of good proportions for eating. Several of these have been circulated to interested parties for and have been favorably received. They could probably be coated with chocolate or other ma terial, or dusted with starch to reduce hygroscopicity and eaten like candy, or perhaps blended with some ingredient to make them fracture and fragment easily and then be used to make juice. They might also be used as a compact chewable form of citrus for space flights and the like. In summary, the conditions for densification of orange and grapefruit foam-mat dried crys tals have been studied. Generally, the lower the moisture content the higher the pressure required for densification of orange, up to 15,. For grapefrut 1,8 psi was optimum with each moisture level studied, and 1.% was the opti mum moisture level. A coincidental result of the study was the observation that these discs might provide a new product form for citrus. LITERATURE CITED Berry, R. E., O. W. Bissett, C. J. Wagner, Jr., and M. K. Veldhuis 167, "Conditions for producing foam-mat dried grapefruit crystals." Food Technol., 1(), 75. Berry, R. E., O. W. Bissett, C. J. Wagner, Jr., and M. K Veldhuis 165, "Foam-mat dried grapefruit powders. tssje S K1 KdH: M. Wrfeht, 154. "Application of formamide as an extraction solvent with Karl Fischer re agent for the determination of moisture in some food pro ducts." Food Technol., 8, 7. AN IMPROVED METHOD FOR MEASUREMENT OF PULP CONTENT OF CITRUS JUICES1 M. D. Maraulja and R. W. Barron Florida Citrus Commission University of Florida Citrus Experiment Station Lake Alfred Abstract Modifications were made to the currently used standard centrifugal for determin ing sinking pulp in reconstituted frozen concenlcooperative research by the Florida Citrus Commission and the Florida Citrus Experiment Station. Florida Agricultural Experiment Stations Journal Series No. 88. trated orange juice as described in the Florida Citrus Commission Regulation Seventyfour of commercial frozen concentrated orange juice, packed during the and citrus seasons, were tested by both the standard and modified s. The were chosen from each season's to provide primarily a wide range of apparent and relative serum viscosities. Comparison of data indicated that precision or "repeatability", using the modi fied, was better than that when the standard was used. In general, precision was better with low viscosity juices regardless of the used.

2 MARAULJA AND BARRON: PULP CONTENT 85 Introduction Experimental Procedures The centrifugal for determining the percentage by volume of free and suspended pulp in frozen concentrated grapefruit juice has been used as a standard procedure by the industry since 14 (7, 8). Little has been done toward improving this, because it was reliable enough for processed grapefruit products. When a limit of not more than 1% sinking pulp was made a requirement for frozen concentrated orange juice in Regulation by the Florida Citrus Commission () in 166, there arose some concern about the low degree of precision of the standard. An improvement in the proce dure or a new approach to the measurement of sinking pulp became important. This study was undertaken to investigate modifications in the standard to improve precision. Review of Literature Olsen and Asbell (5) showed that the use of a Waring Blendor or a colloid mill to size the pulp particles in citrus concentrates, prior to reconstitution, gave more consistent measurement of pulp content. However, this made juice deaeration necessary, which required additional time. They also reported that the percentage of pulp by volume, using the centrifugal, was less after the pulp particles were reduced in size because these smaller particles were packed to gether more closely during centrifugation. A report to the Citrus Products Committee of the Institute of Food Technologists () pointed out that the calibrations on short conical cen trifuge tubes were often inaccurate. Gray (L. E. Gray, FMC Corporation, Lake land, Florida. Private Communication) found that the pulp content in reconstituted citrus con centrates, as determined by the centrifugal, varied approximately 1% by volume when a change of 1 F. occurred in juice tem perature. The amount of pulp in citrus concentrates also influences some of their other characteris tics. Rouse at al (6) showed that the pectinesterase activity is proportional to the pulp content in frozen concentrated orange juices. Maraulja et al. (4) reported that both high pulp and water-insoluble solids contents of frozen concentrated orange juices cause both high ap parent and serum viscosities and that they are proportional to the quantity of serum pectin. Collection of. Seventy-four of commercial frozen concentrated orange juice in 6 or 1 oz cans were selected from 74 processed during citrus seasons. These were packed in 5 Florida plants on approximately February 15, 166, and January 1, February 15, and June 1, 167. Methods of analysis. To obtain data for comparison of the standard and modified meth ods for measuring the sinking pulp content of reconstituted frozen concentrated orange juice, the following procedures were used. Each sample of -6 oz cans from a pack of commercial frozen concentrated orange juice was thawed in running tap water and then accurately reconstituted with volumes of water. This reconstituted juice was then stirred for min utes, immediately after which the coarse or non-sinking pulp was removed by pouring the juice through a standard mesh stainless steel screen, having a wire diameter of.16 inch and a.4 inch opening. One ml portion of the screened reconstituted juice was then removed from each sample and set aside to be used later for the modified. The juice temperature was adjusted, if necessary, to 77 F ± 1 prior to centrifugation. All of the 5 ml centrifuge tubes used in these tests were long conical type and had been previously calibrated for accuracy. Using the standard, tfe sinking pulp content was determined by filling a 5 ml grad uated centrifuge tube with the screened recon stituted juice and then centrifuging at 11 rpm for 1 minutes using a Size 1, Model SBV Inter national Centrifuge. The milliliter reading at the top of the pulp layer was multiplied by to obtain the percentage, by volume, of sinking pulp. Using the modied, 75 ml of distilled water were added to the ml of screened reconstituted juice, previously set aside for this purpose, and this mixture, corresponding to a 1 _j_ 4 dilution of the concentrate, was stirred for just seconds. After adjusting the temper ature to 77 F ± 1, a 5 ml aliquot was filled into each of centrifuge tubes and centrifuged as in the standard. The milliliter read ings at the top of the pulp layers were added together, in this case, to obtain the percentage, by volume, of sinking pulp. When either the standard or modified was used, duplicate determinations were made

3 86 FLORIDA STATE HORTICULTURAL SOCIETY, 167 on each of -6 oz cans from the same pack of orange concentrate. A Brookeld LVT viscometer with the No. spindle was used to measure the apparent vis cosity (1) of the concentrates at 8 F. The readings were taken after 1 minute at 1 rpm. The relative serum viscosity of the reconstituted juices was determined at 8 F with the same instrument using the UL adapter. The readings were taken after 1 minute at 6 rpm. Results and Discussion Average percentages, by volume, of sinking pulp are presented in Table 1, for 74 from of commercial frozen concentrated orange juice processed on approximately 4 dates during citrus seasons. These values were de termined either by the standard or modified meth ods. Each value in Table 1 is the average of 4 determinations. If the range or difference be tween the maximum and minimum of the 4 determinations of the sinking pulp content was 1% or more, it is indicated by an asterisk. Since all individual values for sinking pulp were read to the nearest.5%, regardless of the used, the variations in the ranges of those values on which the other averages are based was within.5%. A comparison may be made of the repeat ability of the results obtained by the s from the frequency distribution of the ranges in sinking pulp values shown in Table. No variation in the ranges was found in a larger percentage of the and variations of 1% or more in a smaller percentage of them when the modified was used. The relative number of average values marked with an asterisk (Table 1) and the per centages of with ranges of 1% or more between 4 determinations, (Table ), indicate that the precision or repeatability of results ob tained using the modified was better than that when the standard was used. Statistical analysis. Sinking pulp values ob tained by the s were analyzed by sta tistical s discussed by Kramer and Twigg () for determining precision or the ability to duplicate results ("repeatability"). They sug gest the use of relative precision, instead of the coefficient of variability, where different s are compared which vary substantially in their mean values. This is the case with the standard and modified s used in this study. The Table 1. Comparison of average sinking pulp values for commercial frozen concentrated orange juices determined by both the standard and modified s. % pulp by volume - average of 4 determinations on can sample l-l Sample * * * * * * ^ 7.4'f *.5 8.* 1.8* * 1.* ^ 1.5* * * 1. 1.* lw.5* * 1.5* * * * * 14.5* 1.6* Difference between minimum and maximum values or range for these was 1.% pulp by volume or more. 8.5* 1.t 11.* 8.* 8.6*.5*

4 MARAULJA AND BARRON: PULP CONTENT 87 Table. Frequency distribution of range in sinking pulp values for commercial frozen concentrated orange juices determined by both the standard and modified s : Range S tandard % pulp by vol. 7 of or more Totals 1. C relative precision is the ratio of the standard deviation among replicates to the range among sample means. The standard deviation was de termined by the least squares. The rela tive precisions are shown below for both s determined from the data for all of concentrates packed on 4 dates in 166 and 167. Date packed /15/66 1/1/67 Method used precision - % Date packed /15/67 6/1/67 Method used precision - % The relative precision of the modified was greater, in all instances, than that of the standard. Conversion factor between s. The conversion factor of 1.5 between the s was calculated by dividing the sum of all of the sinking pulp values, obtained by the standard, by the sum of those found using the modified. Thus, any pulp value deter mined by the modified could be multiplied by 1.5 to obtain the corresponding standard value. This conversion factor of 1.5 is approximately the same as the dilution factor between the s when 4 or volumes of water are mixed with the concentrate prior to centrifugation. Importance of relative serum viscosity. serum viscosity, which is dependent upon the pectin content of the serum centrifuged from a reconstituted juice, was found to be a major factor affecting the precision of the stand ard. Reducing the relative serum vis cosity by the addition of 4 volumes of water to the sample of concentrate results in a closer and more consistent packing of the insoluble pulp particles in the centrifuge tube which makes pos sible greater accuracy in the pulp readings. The effect of serum viscosity on the range of sinking Table. Comparison of s showing effect of serum viscosity on range of sinking pulp values for frozen concentrated orange1 juices packed on February 15, 166. Number of serum viscosity CP8 Total Range of 1% pulp or more Total Range of 1% pulp or more Totals 1

5 88 FLORIDA STATE HORTICULTURAL SOCIETY, 167. Table-4. Effect of temperature on sinking pulp values determined by the standard Apparent % pulp by volume*- standard Sample viscosity- Duplicate determinations Average values cps 6 F. 7 F. 8 F. 6 F. 7 F. 8 F , , , 1, , , , , 1. 1., , 1. 1, , , , % pulp by volume - average decrease per 1 F pulp values, when both s are used, is shown in Table. The relative serum viscosities of the reconstituted juices used varied from less than.4 to. cps. When the standard was used, a range of 1% or more in the sinking pulp values was found in 1 or 5% of the, whereas using the modified, results showed that only or 15% of the values had a range of 1% or more. Regardless of the used, the ratio of the number of values obtained to those having ranges of 1% or more was about the same for in the.5 to. cps group. Effect of temperature on sinking pulp values. Data reported in Table 4 indicate the effect of the temperature on sinking pulp values of recon stituted juices from 4 of frozen concen trated orange juice having apparent viscosities ranging from 86 to 16 cps. Prior to centrifugation, the temperatures of the juices were ad justed to 6, 7, and 8 F. For each 1 de grees increase in temperature, the average decrease in the amount of sinking pulp, as determined by the standard, for all sam ples was.75% by volume. These results are consistent with those reported by Gray. The differences in apparent viscosities of the concen trates had no practical effect on the results obtained when different temperatures were used. Summary High serum viscosity of reconstituted com mercial frozen concentrated orange juices ap pears to be the greatest cause of inconsistent results using the standard centrifugal for determining sinking pulp. Reconstituting the concentrates with four parts of water and centrifuging -5 ml aliquants increased the preci sion of the test. Temperature also has an effect on the pulp values obtained but the pulp level is affected rather than the repeatability of results. LITERATURE CITED 1. Ezell, George H. and Robert W. Olsen Effect of stabilization temperature on the viscosity and stability of concentrated orange juice. Proc. Florida State Hort. Soc. 71: Florida Citrus Commission, Lakeland, Florida. Regu lation January, Kramer, Amihud and Bernard A. Twigg. 16. Fun damentals of Quality Control for the Food Industry. The Avi Publishing Company, Inc., Westport, Connecticut. 4. Maraulja, M. D., R. W. Barron, R. L. Huggart, E. C. Hill, R. W. Olsen, and F. W. Wenzel. 16. Characteristics of commercial frozen orange concentrate packed during sea sons when freezes occurred in Florida. Proc. Florida State Hort. Soc. 76: Olsen, R. W. and Dorothy M. Asbell De termination of the pulp content of concentrated citrus juices. Proc. Florida State Hort. Soc. 74: Rouse, A. H., C. D. Atkins, and R. L. Huggart Effect of pulp quantity on chemical and physical properties of citrus juices and concentrates. Food Technol. 8: United States Department of Agriculture, Agricul tural Marketing Service, United States s for grades of frozen concentrated grapefruit juice. December 8, 156. Washington, D. C. 8. United States Department of Agriculture, Production and Marketing Administration. United States s for grades of canned concentrated orange juice. August 16, 14. Washington, D. C.. Wenzel, F. W. 15. Determination of pulp content of concentrated citrus juices. Mimeo report to Committee on Citrus Products of the Institute of Food Technologists. June 1.