RECENT STUDIES OF THE EFFECT OF PECTINESTERASE ON THE STABILITY OF FROZEN CONCENTRATED ORANGE JUICES

Transcription

1 ROUSE, ATKINS, MOORE: PECTINESTERASE STUDIES 223 Summary Information as to the number of seeds per fruit, the per cent of seeds in the fruit and the amount of moisture in the seeds was deter mined for four common varieties of grapefruit at different stages of development. Seed oils from these samples were found to have physical and chemical values so close as to make dif ferentiation between varieties impossible. How ever, an increase in fruit size resulted in a noticeable increase in refractive index and Hanus iodine absorption number with some in dication that these values may decrease beyond full maturity. The close relationship between refractive index and iodine number would in fer the possibility of using this index as a rough measure of the degree of unsaturation in grapefruit seed oils. Design data for the construction of a smallscale laboratory seed oil press were described as well as procedures and parameters for the gas chromatographic analysis of citrus seed oils. The fatty acid chromatographic analyses of grapefruit seed oils from different varieties and of different maturity showed only small varia tions. A typical analysis for the fatty acid com ponents was established since it was different than that reported in earlier work (4). Fatty acid content, refractive indices and iodine numbers were noticeably similar for shaddock and grapefruit seed oils such as to ad ditionally support a definite relationship be tween the two kinds of citrus fruits. LITERATURE CITED issue ^9589raPh Research Notes- Mlcro fat analysis. Fall 2*l Association of Official Agricultural Chemists. Official methods of analysis 7th Ed., 910 pp Washington, D. C. 3. Fudge, R. B. Relation, of magnesium deficiency in grapefruit leaves to yield and chemical composition of fruit. Fla. Agr. Expt. Sta. Bui. 331: Jamieson, G S., W. F. Baughman and S. I. Gertler. Grapefruit Seed Oil. Oil and Fat Industries 7: Kesterson, J. W. and R. Hendrickson. Naringin, a bitter principle of grapefruit. Fla. Agr. Expt. Sta Bui. 511: Nolte, Arthur J. and Harry W. von Loesecke. Grape fruit Seed Oil, Manufacture and Physical Properties. Ind. and Eng. Chem. 32: RECENT STUDIES OF THE EFFECT OF PECTINESTERASE ON THE STABILITY OF FROZEN CONCENTRATED ORANGE JUICES A. H. Rouse, C. D. Atkins and E. L. Moore Florida Citrus Experiment Station Lake Alfred In 19, the authors (8) reported that frozen orange concentrates prepared from Valencia oranges maintained cloud stability for 52 days or more when placed at 40 F. storage. This was accomplished, regardless of finisher pres sures used during processing, by inactivating the enzyme, pectinesterase (PE), in the juice prior to concentration and by controlling the PE activity in the pulpy cutback juice. Bissett and Veldhuis (4) extracted Valencia orange juice at varying finisher pressures and reported that heating juices to 190 F. was effective in stabilizing the cloud in concentrates pre pared from juices at 5 and 6 psig finisher pres- * Cooperative research by the Florida Citrus Experiment Station and Florida Citrus Commission da Agrlcultural Experiment Station Journal Series, No. sures but was not effective at higher finisher pressures of 7 and 8 psig. The PE activity was approximately the same in the finished products when the juices were heated to 190 F. prior to concentration. Wenzel, Moore, Rouse and Atkins (9) showed that concentrate produced from unheated juices of seedy varieties of citrus are more susceptible to gelation and clarification than those made from juices of the less seedy varieties. Because of this and since the pre viously mentioned studies were made using Valencia orange concentrates, Pineapple oranges were selected for this study. One of the purposes of this paper is to show the ^effect of different PE levels in 42 and 50.7 Brix Pineapple orange concentrates on the stability of these products during storage at 40 F. Concentrates were prepared from juices obtained by using different finisher head pressures. Data are also presented on the pectic contents and water insoluble solids found

2 224 FLORIDA STATE HORTICULTURAL SOCIETY, 1961 initially in these 42 and 50.7 Brix products. Another purpose of this report is to compare the stability of concentrates prepared from evap orator feed juices in which the PE was com pletely inactivated prior to concentration with that of products from evaporator feed juices in which PE was not completely inactivated. The PE activity in the 42 and 50.7 Brix con centrates was carefully adjusted so that these products contained approximately the same amount of enzyme at the different levels of activity used. This was accomplished by using either cutback juices or evaporator feed juices as the only source of PE for the concentrates. Experimental Procedure Preparation of Experimental Packs. Pine apple orange concentrates of 42 and 50.7 Brix, each prepared by using varying finisher pressures and with 3 levels of pectinesterase activity, were processed in the pilot plant at the Florida Citrus Experiment Station. Juice was extracted from grove run oranges using a Brown Citrus Machinery Corporation extractor, Model 400, with a finisher attached and equipped with a 0.0 inch screen. Four runs were made with pressure head settings of 5, 10, psig. Juices were deaerated, heated to 0 F. in a Walker-Wallace platetype heat exchanger and concentrated to 55 Brix in the Atkins Model A evaporator (1). Complete pectinesterase inactivation was ob tained in the juices heated to this temperature. Distilled water and a prepared pulpy juice with known PE activity were added so that the finished products were 42 and 50.7 Brix. One third of the concentrates prepared con tained about unit, another third about units and the last third about units of PE per gram of concentrate. Pulpy juice was obtained by collecting the underflow when centrifuging the finisher juice through a Westfalia Separator with a 50 sec ond cycle setting. The underflow juice was filled in 6-ounce cans, sealed and immediately placed in front of the air blast in the 8 F. storage room. Thereafter, each morning while proc essing, the proper number of cans of frozen pulpy juice was thawed for 1 hour in running water and some of the cans heated in boiling water for minutes to inactivate the PE. These heated cans were then cooled in running tap water and kept refrigerated along with other unheated cans until the pulpy juice was used as cutback. By the addition of proper volumes of either heated or unheated cutback juice, 3 levels of PE were obtained in the 42 and 50.7 Brix concentrates. Thus, 3 series (4 packs each) of both 42 and 50.7 Brix concentrates were prepared from the same lot of thoroughly mixed Pine- Table 1. Characteristics of 42 and 50.7 Brix Pineapple orange concentrates containing different levels of pectinesterase activity and made from juices prepared with varying finisher pressures Finisher pressure psig (PE.uo)g concentrate* X1000 HoO Pectin (» as AGA1 -- mer/100 e soluble in NaOH Total Water-insol. solids mg/100 g Relative viscosity at 26 C. of serum from reconsto juice 4.2 Brix concentrates U « HO O Brix concentrates Anhydrogalacturonic acid. 2 only source of pectinesterase was unheated pulpy cutback juices.

3 ROUSE, ATKINS, MOORE: PECTINESTERASE STUDIES 225 apple oranges by processing juices that were ex tracted separately using varying finisher pres sures. One series contained unit, another units and the third series units of PE, the source of which was only the cutback juices. Six additional packs of concentrates were prepared from juices in which PE activity was present during concentration. Two juices were prepared as before with finisher pressures of 5 and psig. Quantities of these orange juices heated to 0 F. were blended with sufficient amounts of their respective unheated juices so that the concentrated juices contained units of PE activity per gram of 42 or 50.7 Brix products. Another mixture of heated and unheated juices, using only juice prepared with a finisher pressure of psig, was evaporated resulting in concentrates having PE units per gram of 42 or 50.7 Brix products. Similar amounts of pulpy cutback juices with com pletely inactivated PE were used to maintain approximately the same pectic content. In these concentrates the source of the pectinesterase was the unheated portion of the evap orator feed juice. Thawing of Sa?nples.-Cans of 42 and 50.7 Brix concentrates were removed from the 8 F. storage room and thawed for 1 hour on a rotary thawer at 40 F. Cans of thawed con centrates were placed at 40 F. storage and examined at periodic intervals. Samples of con centrate used for initial analysis were thawed by submerging the 6-ounce cans in running tap water, about 80 F., for 30 minutes. Methods of Analysis. Pectinesterase activity (6) is expressed by the symbol (PE.u.) g which represents the milliequivalents of ester hydrolyzed per minute per gram of concentrate and multiplied by 1000 for easy interpretation. Pectin was divided into water-, ammonium oxalate- and sodium hydroxide- soluble frac tions and each of these pectic fractions was determined as anhydrogalacturonic acid (AGA) by an adaptation of the Dische colorimetric method (5, 6). Values are expressed as milli grams of AGA per 100 grams of concentrate. Water-insoluble solids were determined by a modified A.O.A.C. method (7) and expressed as milligrams per 100 grams of concentrate. Cloud or turbidity (2) in the serum of re constituted juice was measured as per cent light transmittance using a Photovolt Lumetron colorimeter, Model No. 402-E, with 10 mm rectangular 14 ml cuvette and filter No An increase in per cent light transmittance atually results from a decrease in cloud and, therefore, is an indication of clarification. Relative viscosity of the serum from recon stituted juice was determined at 26 C. with an Ostwald pipette. Results and Discussions Values reported in Table 1 are the average of those from 2 samples prepared from juices using consecutive finisher pressures, such as 5 and 10 psig representing low pressure and 15 and psig representing high pressure, because no appreciable changes were found in the chemical characteristics of packs when only a difference of 5 psig on the finisher head was used. In preparation of these packs the PE in the juices was inactivated prior to concentration. Pectinesterase in the concentrates resulted from only that in the added pulpy cutback juices. Data in Table 2 are those for the individual packs prepared from juices using finisher pres sures of 5 and psig. In the preparation of these packs PE was present during concentra- Table 2. Characteriatioa of 42 and 50.7 Brix Pineapple orange concentrates prepared from juices containing different levels of peotlnesteraae activity during concentration Finisher pressure psig (PE.u.)g oonoentrate X 1000 Pectin H (* as AGA1 - ag/100 g soluble In IH4)2C2 4 NaOH Total Water-tn«ol. solids Dg/100 g Relative viscosity at 26 C. of serum from reeonst. juloe 42 Brijc concentrates Brix concentrates

4 226 FLORIDA STATE HORTICULTURAL SOCIETY, 1961 tion and no PE was added in the heated pulpy cutback juices. Pectin. Data obtained from the initial ex amination of the 42 and 50.7 Brix frozen Pineapple orange concentrates are presented in Tables 1 and 2. The pectic fractions in the 42 and 50.7 Brix concentrates always in creased as the finisher pressures increased from psig to psig. The average percentage increases in the water-, ammonium oxalate-, sodium hydroxide-soluble and total pectins for 42 Brix concentrates with 3 PE levels were 18.5, 10.9, 6.4 and 11.8, respectively, and for 50.7 Brix concentrates with 3 PE levels they were 15.2, 12.2, 8.9 and 11.8, re spectively. The quantities of water-soluble pectin in these concentrates are comparable to those for commercial samples reported in terms of reconstituted juice by Atkins, Rouse, Moore and Wenzel (3) for midseason samples. Pectin data listed in Table 2 are for the 42 and 50.7 Brix concentrates prepared from juices with finisher pressures of 5 and pisg and with PE units in each. Also, results for 42 and 50.7 Brix products are shown when juices were prepared at psig finisher pres sure and units of PE were in each concen trate. These 2 levels of enzymic activity were present during evaporation of the juices. The amounts of pectic fractions in the concentrates, shown in Table 2, from juices made using psig finisher pressure are slightly higher than for those juices previously extracted. Although these concentrates (Table 2) were prepared from the same lot of fruit, the juices were extracted 4 days later. The increased values may be attributed to differences in this juice because the oranges at room temperature had softened slightly. The larger values of the ammonium oxalate-soluble pectin (Table 2) are believed to be due to the overall increase in total pectin rather than to demethylation of the water-soluble pectin by PE activity present during concentration. Relative viscosity, measured at 26 C. of the serum from reconstituted juices, slightly in creased with increasing finisher pressures be cause water-soluble pectins increased. Slight decreases in serum viscosities were evident (Table 2) when a finisher pressure of psig was used and the concentrates contained similar amounts of water-soluble pectin. The principal differences in these samples were the 2 PE levels of activity, which were present during evaporation of the juices. Water-Insoluble Solids. Amounts of waterinsoluble solids, chiefly indicative of cellulose and protopectin, increased when high finisher pressures were used (Tables 1 and 2). For example, as shown in Table 2, the 42 Brix concentrate prepared from juice when 5 psig finisher pressure was used contained 5 mg/ 100 g of water-insoluble solids, whereas, con centrates prepared from juices using psig had 635 mg/100 g. Similar increases are shown in the 50.7 Brix concentrates. Although pulp contents are not presented in tabular form, this constituent varied from 12 to 17% in the reconstituted juices when finisher pressures varied from 5 to psig. Pectinesterase Activity. Three known levels of PE activity in the concentrates were obtained by the addition of pulpy cutback juices; one at a low enough activity ( unit) which would have little effect on stability of the finished product, another at which the activity ( units) would slowly affect the stability and a third level at which the activity ( units) would probably affect the stability in a few days when the concentrates were stored at 40 F. These levels of PE are equivalent to 1.2, 4.8 and 8.3 units when calculated per gram of soluble solids for a 42 Brix concentrate. The first 2 levels are comparable to the PE found in approximately 90% of the commercial sam ples examined during the season (3). Only 2.4% of these commercial samples con tained PE units greater than 8.0 These same 3 PE levels are equivalent to 1.0, 3.8 and 6.7 units when calculated for a 50.7 Brix con centrate. Two factors, other than PE, were present in these concentrates which had an ef fect on their stability, namely pectic content which was dependent upon the finisher pressure used and the degree of concentration. The 50.7 Brix concentrate, a 5-fold product is in a range of densities within which the citrus processors are currently interested for pre paring a high density orange concentrate. The fact is reiterated that the juices used for the 4- and 5-fold packs (Table 1) had no active PE present during concentration, whereas the juices for preparing the packs (Table 2) were subject to the action of PE during evap oration.

5 ROUSE, ATKINS, MOORE: PECTINESTERASE STUDIES 227 PE UNITS PE UNITS PE UNITS TIME-DAYS AT 40«F. Figure 1. Relationship of 42 Brix concentrates with 3 con trolled PE activity levels to cloud stability during storage at 40 F. Each curve represents 4 packs of concentrates pre pared from juices extracted using finisher pressures ranging from 5 to psig and the PE was completely inactivated prior to concentration PE UNITS 2.OPE UNITS PE UNITS L ' ' TIME OAYS AT 40 *F. EXTREME OEFMITE SLIGHT NONE Figure 2. Relationship of 50.7 Brix concentrates at 3 controlled PE activity levels to cloud stability during storage at 40 F. Each curve represents 4 packs of concentrates pre pared from juices extracted using finisher pressures ranging from 5 to psig and the PE was completely inactivated prior to concentration. PE UNITS ANO 5 pilg 507* Brix* PE UNITS AND ptlg PE UNITS ANO ptlg E OEFINITE s I Storage Effect on the Stability of the Concen trates. Results of a "stability test" based on the storage of the 42 and 50.7 Brix concen trates at 40 F. are graphically presented in Figs. 1, 2 and 3. Samples were examined peri odically during the time of storage for changes in light transmittance and degree of gelation. Figs. 1 and 2 represent the packs made from juices which contained no active PE during concentration and Fig. 3 those packs whose juices contained active PE during evaporation. Each point on the curves in Figs. 1 and 2 is the average optical density, expressed as light transmittance, for 4 concentrates. These prod ucts were made from juices obtained using finisher pressures ranging from 5 to psig and having PE levels at, and units for each concentration. These packs of 42 and 50.7 Brix concentrates containing unit of PE activity showed no appreciable loss of cloud (Figs. 1 and 2 and Table 3) after 132 days of storage at 40 F. The 42 Brix con centrates (Fig. 1 and Table 3) with and units of PE required 33 and 8.5 days, respec tively, to develop definite clarification; how ever, the 50.7 Brix concentrate (Fig. 2 and Table 3) at the PE level showed only slight clarification after 130 days but that ait the PE level developed definite clarifica tion after 67 days at 40 F. storage. Three packs of each of 42 and 50.7 Brix (4- and 5-fold) concentrates with and units of PE were prepared from juices with the pectic enzyme present during evaporation. One pack of each fold was prepared from juice when 5 psig finisher pressure was used and the other 2 packs from juices obtained using psig finisher pressure. The results of the "stability test" are graphically shown in Fig. 3. Again the 50.7 Brix concentrates were more stabilized than the 42 Brix products. Clarification de veloped sooner during storage in those packs, which had similar PE, when the PE activity was present during evaporation (Tables 2 and 3) TIME-DAYS AT 40* F. Figure 3. Relationship of 42 and 50.7 Brix concentrates with 2 controlled PE activity levels to cloud stability during storage at 40 F. Each curve represents a single pack, pre pared from juices using finisher pressures of 5 or psig. containing pectinesterase from evaporator feed juice. Packs of concentrates at 42 and 50.7 Brix which had PE of unit indicated no appreci able changes in stability after extended storage. Also greater stabilization was among the 50.7 Brix concentrates to which were added and units of PE. The effect of concentration in hibiting enzymic activity during storage at 40 F. was definitely indicated by the increased

6 228 FLORIDA STATE HORTICULTURAL SOCIETY, 1961 stability of the 5-fold over that of the 4-fold products. Effect of Finisher Pressure on the Stability of Orange Concentrates. At the PE level, finisher pressure (Table 3) did not affect the cloud stability of the concentrates when PE was not present during concentration. Con centrates from juices prepared with a finisher pressure of psig were stabilized to the same extent as those from juices prepared with 5 psig. Similar results were observed by the authors (8) when using Valencia orange juice. However, concentrates from juices finished at psig and with a portion of their initial PE activity present during evaporation were less stabilized than the products prepared from juices finished at 5 psig and containing similar activity during evaporation. Gelation was not observed in the concentrates having PE units during the 132 days storage at 40 F. In the products with and levels of PE in this series, nothing greater than slight gela tion (No. 2 gel) occurred. However, undesir able semi- and solid gels (No. 3 and 4 gels^ resulted during storage in the 42 and 50.7 Brix concentrates containing and PE units when the juice was prepared with psig finisher pressure and when active PE was present during concentration. For ex ample, a semi-gel occurred at the PE level in the 5-fold product after 28 days at 40 F., while the cloud in the reconstituted juice was satisfactory since its light transmittance was 54.5%, and a solid gel formed after 42 days when the light transmittance was 7%. Summary Twelve packs of 42 Brix Pineapple orange concentrates were prepared from juices ob tained by using 4 different finisher head pres sures and heated to 0 F., prior to concen tration to completely inactivate pectinesterase. Cutback juice of known pectinesterase activity was added so that the 4 concentrates contained about, and units per g of con centrate. Corresponding packs of 50.7 Brix concentrate were prepared from the same juices. In these 24 packs when the PE was inactivated in the evaporator juices no differences were ob served on initial examination of the concen trates. The 42 and 50.7 Brix concentrates with PE unit of activity did not lose cloud after 132 days at 40 F. storage; those with PE required 33 and more than 130 days, respectively, to develop definite clarification; and those with the PE level required 8.5 and 67 days, respectively, before definite clarifi cation was detectable. Three packs of 42 Brix Pineapple concen trates were prepared from juices using 5 or psig finisher head pressures. During evapora tion 2 of the concentrated juices had pec tinesterase activity equivalent to units and the other equivalent to units per g of con centrate. The cutback juice was completely in activated of enzymic activity. Corresponding packs of 50.7 Brix concentrates were also pre pared from the same juices. In these 6 packs, both the 42 and 50.7 Brix concentrates were less stabilized during 40 F. storage than those products to which PE activity was added only in Table 3. Number of days required for development of definite clarification1 in Pineapple orange concentrates containing pectinesterase from either cutback juices or evaporator feed juices Source of PE No PE present during concentration PE added after concentration in cutback juice PE from evaporator feed juice present during concentration No PE added after concentration Number of concentrates (PE.u.)g concentrate X 1000 Finisher pressure-psig Time in days2 U 4 See footnote 2 4,2 Brix orange concentrates stored at 1 5 > o Q onncentrates stored at AO F, 1 1 Time in days2 >132 > Definite clarification indicated by light transmittance in the range of 70-8$ for centrlfuged, reconstituted juice using Lumetron colorimeter, Model 402-E, filter No. 730 and 14 ml cell. 2 Values for this group of concentrates are results or averages of data obtained concerning A concentrates made from juices obtained using finisher pressures of 5, 10, psig.

7 DENNISON: SEBAGO CHIPPING QUALITIES 229 cutback juices. Also varying finisher pressures used in preparing the juices definitely affected the stability of the finished products when stored at 40 F. Data from the 30 packs indicated that as fin isher pressures increased from 5 to psig, the water-soluble, ammonium oxalate-soluble and sodium hydroxide-soluble pectins increased in the juices. Water-insoluble solids in the con centrates also increased with increased pres sures and, in general, the relative serum viscosi ties increased with water-soluble pectin. In all cases the 50.7 Brix concentrates re mained stabilized in 40 F. storage much longer than did the 42 Brix packs with similar activ ity. This demonstrated the effect of concentra tion caused by inhibiting the PE activity. LITERATURE CITED 1. Atkins, C. D., F. W. Wenzel and E. L. Moore Report new technical strides in design of FCC evaporator. Food Industries 22: 1353, 1466, Atkins, C. D., A. H. Rouse and E. L. Moore Determination of cloud retention in frozen concentrated orange and grapefruit juices with various colorimeters. Proc. Florida State Hort. Soc. 68: Atkins, C. D., A. H. Rouse, E. L. Moore and F. W. Wenzel Comparison of some characteristics of commer cial frozen concentrated orange juices prepared by Florida processors during five citrus seasons. Proc. Florida State Hort. Soc. 72: Bissett, O. W. and M. K. Veldhuis Effects of finisher pressure on characteristics of Valencia orange con centrate. Proc. Florida State Hort. Soc. 69: Dische, Z A new specific color reaction of hexuronic acids. Jour. Biol. Chem. 167: Rouse, A. H. and C. D. Atkins Pectinesterase and pectin in commercial citrus juices as determined bv methods used at the Citrus Experiment Station. F orida Aqr. Exp. Sta. Tech. Bui Rouse, A. H. and C. D. Atkins Methods for estimation of insoluble solids in citrus juices and concentrates. Proc. Florida State Hort. Soc. 68: Rouse, A. H., C. D. Atkins and E. L. Moore. 19. Effect of pectinesterase on the stability of frozen concen trated orange juice. Proc. Florida State Hort. Soc. 73: Wenzel, F. W., E. L. Moore, A. H. Rouse and C. D. Atkins Gelation and clarification in concentrated citrus juices. I. Introduction and present status. Food Technol. 5: INFLUENCE OF MATURITY AND STORAGE CONDITIONS ON CHIPPING QUALITIES OF SEBAGO POTATOES R. A. DENNISON Florida Agricultural Experiment Station Gainesville Many potato chippers like to use freshly harvested southern-grown potatoes because light colored chips can be made from the tubers. Large quantities of northern-grown potatoes are stored to extend the period of use, but stored southern potatoes are considered un acceptable for chipping. For the southern pota toes storage time is usually short, if consider able deterioration is to be avoided, and the potatoes do not recondition to give light colored chips. Darker colored chips result as the reducing sugar content of the tubers increases (6). Sev eral workers have shown that conditions other than reducing sugar levels in the tubers have a controlling effect on the ultimate chip color. Shallenberger et al. (4) found that chip color correlated with both reducing sugars and sucrose. Habib and Brown (2) showed that the level of some of the amino acids, especially the basic amino acids, influenced the color of the chips. Florida Agricultural Experiment Stations Journal Series, No Florida-grown potatoes are not likely to be stored for long periods at low temperatures (40 F) such as those used for northerngrown potatoes, but at times Florida potatoes are held under varying storage conditions for limited periods. The present study was under taken to determine the influence of short storage intervals on certain changes in sugar content and chipping quality of Florida- (Hast ings area) grown potatoes harvested at two periods in the latter half of a normal season. Previous studies (1) showed that potatoes harvested in Florida during the early part of the season responded differently from those harvested later. Experimental Procedure Two lots of potatoes of the Sebago variety were obtained from the Hastings area. One lot was harvested May 25 and the other June 2, 19. The first lot was representative of tubers from the latter part of the mid-season harvesting and the second lot represented late harvested tubers. Samples consisting of approximately 4500 grams of the tubers were placed in ventilated fiberboard boxes for storage. Tubers from each harvest were stored at 50 and 57.5 F and maintained at approximately 85% relative humidity. The tubers were held at the two