Anthocyanin and colour changes during processing of pomegranate (Punica granatum L., cv. Hicaznar) juice from sacs and whole fruit

The effects of clarification and pasteurisation on anthocyanins (ACNs) and the colour of pomegranate juice (PJ) produced from sacs and whole fruits were investigated. Clarification caused a loss of 4% of ACNs in juice from sacs (JFS) and a loss of 19% in juice from whole fruit (JFWF). After pasteurisation, there was an 8–14% and 13–9% loss of ACNs from unclarified and clarified JFS and JFWF samples, respectively. Polymeric colour was very high even in unclarified samples (25–29%). Compared to JFS, higher polymeric colour was formed in JFWF. HPLC analyses of PJ revealed that cyanidin-3,5-diglucoside was the major ACN, followed by cyanidin-3-glucoside and delphinidin-3-glucoside. Cyanidin-3,5-diglucoside showed higher stability to clarification and pasteurisation than cyanidin-3-glucoside in both PJ samples. Cold clarification with only gelatin is recommended for PJ. To prevent excessive ACN loss and the formation of brown colouring, PJ should be subjected to minimal heating.     

Kinetics of anthocyanin degradation and polymeric colour formation in black carrot juice concentrates during storage

The changes in anthocyanins (ACNs) and polymeric colour of black carrot juice concentrate (BCJC) samples were monitored during storage at ?23, 5 and 20 °C for 319 days and at 30 °C for 53 days. While ACN degradation was fitted to a first‐order reaction model, polymeric colour formation was fitted to a zero‐order reaction model during the storage. Half‐life periods for ACN degradation in BCJCs were 603, 137 and 29 days at 5, 20 and 30 °C, respectively. The reaction rate constants for polymeric colour formation were 0.0207, 0.1435 and 0.5581%/days at 5, 20 and 30 °C, respectively. HPLC‐MS analyses of BCJC showed that cyanidin‐3‐galactoside‐xyloside‐glucoside‐ferulic acid (56%) was the major ACN, followed by cyanidin‐3‐galactoside‐xyloside (19%) and cyanidin‐3‐galactoside‐xyloside‐glucoside‐sinapic acid (10%). Cyanidin‐3‐galactoside‐xyloside‐glucoside‐ferulic acid was the most stable ACN in BCJC at storage temperatures. BCJCs should be kept at sub‐freezing temperatures to minimise ACN degradation.     

Viscous Food Matrix Influences Absorption and Excretion but Not Metabolism of Blackcurrant Anthocyanins in Rats

ABSTRACT:  The aim of the present study was to investigate the effect of a simultaneous intake of food and anthocyanins (ACNs) on ACN absorption, metabolism, and excretion. Blackcurrant ACNs (BcACNs) were dissolved in water with or without the addition of oatmeal and orally administered to rats, providing approximately 250 mg total ACNs per kilogram BW. Blood, urine, digesta, and tissue samples of the stomach, jejunum, and colon were subsequently collected at 0.25, 0.5, 1, 2, 3, 7, and 24 h. Identification and quantification of ACNs were carried out by Reversed phase-high-performance liquid chromatography (RP-HPLC) and liquid chromatography-mass spectrometry (LC-MS). Four major ACNs were present in the blackcurrant extract: delphinidin 3- O -glucoside, delphinidin 3- O -rutinoside, cyanidin 3- O -glucoside, and cyanidin 3- O -rutinoside. In plasma, the 4 ACNs of blackcurrant were identified and quantified. The time to reach maximal total ACN plasma concentration ( C _max BcACN/water = 0.37 ± 0.07 μmol/L; C _max BcACN/oatmeal = 0.20 ± 0.05 μmol/L) occurred faster after BcACN/water ( t _max= 0.25 h), than after BcACN/oatmeal administration ( t _max= 1.0 h). In digesta and tissue samples, the 4 original blackcurrant ACNs were detected. The relative concentration of rutinosides in the digesta increased during their passage through the gastrointestinal tract, while the glucosides decreased. Maximum ACN excretion in urine occurred later after BcACN/oatmeal than after BcACN/water administration (3 compared with 2 h). The 4 original ACNs of blackcurrant in their unchanged form, as well as several metabolites, were identified in the urine samples of both groups. The simultaneous intake of food affects ACN absorption and excretion in the urine, but not metabolism.     

Anthocyanin profile of mayhaw (Cretaegus opaca)

Mayhaw samples (Elite 2001, Texas Star 2000 and 1999) were harvested over a three-year period and analyzed for anthocyanin concentration, colour density, polymeric colour, and % polymeric compounds. Anthocyanins were separated by HPLC. All mayhaw samples from the three year period contained about 50% of cyanidin-3-glucoside, 10–21% cyanidin-3-galactoside, and less than 32% unidentified anthocyanins. The highest concentration of anthocyanins was detected in the Texas Star 1999 sample (about 7 mg/100 g) whereas Texas 2000 and Elite 2001 had 3.3 and 2.3 mg/100 g of anthocyanins, respectively. Colour density was lower in the Elite samples than the Texas. The polymeric anthocyanins and polymeric colour decreased in the Elite 2001 > Texas Star 2000 > Texas Star 1999 and the decrease was tentatively ascribed to sample age.     

Influence of clarifying agents on the quality of pasteurised palmyra palm sap (Borassus flabellifer Linn.)

The effects of clarifying agents, including bentonite, polyvinylpolypyrrolidone (PVPP), gelatin and chitosan, on the quality attributes of pasteurised palmyra palm sap were evaluated. After clarification and pasteurisation, the lowest polyphenol oxidase (PPO) and invertase activities were detected in the sample clarified with bentonite. PVPP and gelatine were found to be the most effective for removing polyphenol content. In addition, the sample treated with chitosan had the highest transmittance values. However, the sucrose, glucose and fructose contents were not affected by clarification. During storage, the PPO activity, invertase activity, polyphenol content and sucrose level decreased, while the fructose and glucose levels increased with the storage times. According to the Thai Community Product Standard, all pasteurised samples treated with a clarifying agent were acceptable for up to 25 days, whereas the nonclarified sample was spoiled because of the microbial loads. Thus, the clarification process prior to pasteurisation was able to improve the quality and microbiological shelf life of the pasteurised palmyra palm sap for at least 25 days.     

The effects of six phenolic acids and tannic acid on colour stability and the anthocyanin content of mulberry juice during refrigerated storage

Six phenolic acids and tannic acid are added to fresh mulberry juice to enhance the colour. Effects of these copigments on colour stability and the anthocyanin content of mulberry juice are investigated while being stored at 4 °C for 30 days. Results suggest that the addition of the copigments markedly increases the maximum absorbance of mulberry juice. Cyanidin-3-glucoside is the major anthocyanin, followed by cyanidin-3-rutinoside. Furthermore, the retention rate of the total anthocyanin, cyanidin-3-rutinoside and cyanidin-3-rutinoside increases after the addition of all copigments. The effect of ferulic acid on the stability of total anthocyanin, cyanidin-3-glucoside and cyanidin-3-rutinoside in mulberry juice is the best, 89.52%, 86.90% and 94.46% respectively (66.56%, 62.58% and 73.60% in the control group). Researchers recommend the addition of ferulic acid, p-coumaric acid and caffeic acid – all of which belong to the hydroxycinnamic acid group, to the mulberry juice to enhance the colour stability and anthocyanin content.     

In vitro absorption and antiproliferative activities of monomeric and polymeric anthocyanin fractions from açai fruit (Euterpe oleracea Mart.)

Anthocyanins are among the most important and widely consumed natural pigments in foods, and have attracted increased attention as natural food colourants and potent bioactive agents. However, anthocyanins are generally unstable and may undergo chemical changes that include oxidative and polymerisation reactions during processing and storage. The role of anthocyanin polymerisation reactions on in vitro intestinal absorption and anti-cancer properties has not been assessed. This study investigated the chemical composition, antioxidant properties, antiproliferative activity, and in vitro absorption of monomeric and polymeric anthocyanin fractions from açai fruit (Euterpe oleracea Mart.). Cyanidin-3-rutinoside (58.5 ± 4.6%) and cyanidin-3-glucoside (41.5 ± 1.1%) were the predominant compounds found in monomeric fractions, while a mixture of anthocyanin adducts were found in polymeric fractions and characterised using HPLC–ESI-MSⁿ analyses. Monomeric fractions (0.5–100 μg cyanidin-3-glucoside equivalents/ml) inhibited HT-29 colon cancer cell proliferation by up to 95.2% while polymeric anthocyanin fractions (0.5–100 μg cyanidin-3-glucoside equivalents/ml) induced up to 92.3% inhibition. In vitro absorption trials using Caco-2 intestinal cell monolayers demonstrated that cyanidin-3-glucoside and cyanidin-3-rutinoside were similarly transported from the apical to the basolateral side of the cell monolayers (0.5–4.9% efficiency), while no polymeric anthocyanins were transported following incubation for up to 2 h. The addition of polymeric anthocyanin fractions also decreased monomeric anthocyanin transport by up to 40.3 ± 2.8%. Results from this study provide novel information regarding the relative size, absorption, and bioactive properties of anthocyanin monomers and polymer adducts.     

Effects of various clarification treatments on phenolic compounds and color of apple juice

The purpose of this study was to investigate the changes that occur during conventional clarification using gelatin, bentonite, silica sol, and water-soluble chitosan on the phenolic compounds, antioxidant activity, and color of apple juice. The apple material used in this study was of two varieties: Sampion and Idared. The changes in the polyphenols composition (procyanidins, hydroxycinnamic derivatives, and dihydrochalcones) were monitored through the clarification process. Sampion apple control juices contained more total polyphenols than do Idared apple juices. In Sampion variety apple juice, the dominant polyphenols are the flavan-3-ols (86% of total polyphenols), followed by hydroxycinnamic acids (9.7%), dihydrochalcones (3.0%), and flavonols (1.3%). In Idared apple juice the hydroxycinnamic acids (especially chlorogenic acid) are dominant (about 48% of total polyphenols), followed by flavan-3-ols (40%). However, the concentration of polymeric procyanidins in Sampion apple juices was 62.8 and 46.3% less when the Profloc (chitosan) and gelatin treatments were used, respectively. Aktivbentonit and Puranit (bentonite) supplementary added in juices clarification have some protective effect on polymeric procyanidins only with Profloc treatment. That kind of effect was not observed in Idared apple juices with almost eight times smaller polymeric procyanidins concentration than in Sampion apple juices. The antioxidant activity, measured by the DPPH (1,1-diphenyl-2-picrylhydrazyl radical) method, ranged from 0.20 mg TEAC/mL in Idared apple juice to 0.30 mg TEAC/mL in Sampion apple juice, measured by the ABTS method, from 0.17 to 0.48 mg TEAC/mL, respectively. Clarification of apple juices with chosen clarifying agents has statistically no significant (p>0.05) influence on antioxidant capacity. This study suggests that chitosan can be used as a conventional clarifying aid of apple juices and that treatment has no impact on their biochemical parameters.     

Effects of processing and storage on juice colour and betacyanin stability of purple pitaya (<Emphasis Type="Italic">Hylocereus polyrhizus</Emphasis>) juice

Purple pitaya (Hylocereus polyrhizus) fruits have been recently proposed as a promising source of betalains. In the present study, purple pitaya juice processing at pilot-plant scale is reported for the first time. Each processing step was examined in terms of juice colour and betacyanin retention. Lightness (L ^*) and hue angle (h°) values were strongly influenced by juice filtration, while chroma (C ^*) and betacyanin retention were most strongly altered by pasteurisation. Three systems of juice pasteurisation were evaluated. Betacyanin loss and colour alteration were minimal upon pasteurisation in an HTST system and a standard tubular heat exchanger, respectively. Additionally, storage experiments using mucilage-free purple pitaya juice were conducted. Whereas light exposure of unsupplemented samples resulted in significant pigment degradation, detrimental effects of light exposition were completely prevented by the addition of 1% ascorbic acid prior to storage. After 6 months, about 70% of the initial betacyanin content was retained in the presence of ascorbic acid, irrespective of illumination.     

Combined high-pressure and thermal treatments for processing of tomato puree: evaluation of microbial inactivation and quality parameters

The effects of combined high-pressure thermal treatments on consistency, viscosity, colour, lycopene content, enzyme activity and micro-organisms were determined, and compared to conventional pasteurisation and sterilisation processes of tomato puree. High-pressure processing at ambient temperature (HPP) improved the colour and viscosity compared to heat pasteurisation, while the water binding capacity and lycopene content were unaffected by HPP. Products treated at 700 MPa, 20 °C resulted in inactivation of the natural flora to a level below the detection limit. After pressure treatment and during chilled storage a increase in viscosity was observed. HPP caused partial inactivation of polygalacturonase (70%), but activation of pectin methylesterase. After high-pressure sterilisation treatments combined with elevated starting temperatures (≥80 °C, HPS, one or two pulses) an ambient stable product was obtained. HPS (one pulse, 700 MPa, 30 s, 90 °C) reduced B. stearothermophilus spore contamination level in inoculated meatballs in tomato puree with at least 4.5 log units. HPS resulted in more than 99% inactivation of polygalacturonase and pectin methylesterase. HPS resulted in a lower viscosity compared to conventional sterilised samples, whereas the water binding capacity was improved. Colour appreciation was improved and lycopene content was retained compared to a 40% loss after conventional sterilisation.     

Chemical stability of açai fruit (Euterpe oleracea Mart.) anthocyanins as influenced by naturally occurring and externally added polyphenolic cofactors in model systems

The influence of different classes of naturally occurring and externally added polyphenolic cofactors on the phytochemical and colour stability of anthocyanins in açai fruit (Euterpe oleracea) was investigated. Model systems were based on anthocyanin isolates from açai fruit, rich in cyanidin-3-rutinoside (311 ± 27 mg/l) and cyanidin-3-glucoside (208 ± 18 mg/l), and isolated groups of naturally occurring polyphenolic cofactors in açai fruit (phenolic acids, procyanidins, and flavone-C-glycosides, each adjusted to ∼50 mg/l). Anthocyanin degradation kinetics were assessed as a function of pH (3.0, 3.5, and 4.0) and storage temperature (5, 20 and 30 °C). During storage, anthocyanins experienced pH and temperature-dependent losses, and the half life cyanidin-3-rutinoside (t_1/2 = 2.67–210 days) was consistently longer than cyanidin-3-glucoside (t_1/2 = 1.13–144 days). The presence of flavone-C-glycosides induced significant hyperchromic shifts and enhanced anthocyanin stability at all pH and temperature combinations, while no significant effects were attributed to the presence of phenolic acids or procyanidins. Additional models using externally added cofactors from rooibos tea, also rich in flavone-C-glycosides, resulted in up to 45.5% higher anthocyanin colour and up to 40.7% increased anthocyanin stability compared to uncopigmented anthocyanin isolates and had similar copigmentation effects to a commercial rosemary-based colour enhancer. Results suggest flavone-C-glycosides offer potential for their use as colour enhancers and stabilizing agents in products rich in cyanidin glycosides, particularly açai fruit-containing foods, juice blends, and beverages.     

Anthocyanin and organic acid profiles of pomegranate (Punica granatum L.) juices from registered varieties in Turkey

This is the first study to analyse the profiles of anthocyanin (ACN) and organic acid (OA) and some physico‐chemical properties of pomegranate juices (PJs) obtained from nine registered varieties in Turkey. HPLC analyses revealed that there were significant differences between ACN contents (28–447 mg L^?1) and profiles (P < 0.01). The PJs contain maximum six ACNs, 3‐glucosides and 3,5‐diglucoside of delphinidin, cyanidin and pelargonidin. The major OA in PJs was citric acid (66–74%), followed by malic (6–12%), succinic (5–19%), nonidentified (0–14%) and tartaric acids (0.1–3.7%). Amongst individual OAs, citric acid had the most significant effects on TA (r = 0.9761), pH (r = 0.9208) values and sourness of PJs. As different from literature, results of this study revealed that malic acid contents of authentic PJs could be higher than 1.5 g L^?1. Consequently, ACN and OA profiles could be successfully used in quality control because all PJs have their own typical ACN and OA profiles.     

Phytochemical,antioxidant and pigment stability of açai (Euterpe oleracea Mart.) as affected by clarification,ascorbic acid fortification and storage

Açai juice at two clarity stages (semi-clarified and clarified) was compared to 100% açai pulp following ascorbic acid fortification to evaluate phytochemical and antioxidant changes during storage at 4 and 20 °C. Cyanidin-3-rutinoside (202 ± 5.8 mg/L) and cyanidin-3-glucoside (75 ± 4.8 mg/L) were the predominant anthocyanins in açai while 11 non-anthocyanin polyphenolics were detected in concentrations from 1.1 to 55 mg/L of açai pulp. Clarification of açai pulp resulted in a 27% loss in total polyphenolics (197 ± 6.9 mg gallic acid/100 mL) and in a 20% reduction in both total anthocyanins (729 ± 3.4 mg/L) and antioxidant capacity (54 ± 1.7 μmol Trolox equivalents/mL). Anthocyanin degradation followed first order kinetics, with half-lives ranging from 9.4 to 43 days for cyanidin-3-glucoside and from 18 to 82 days for cyanidin-3-rutinoside. Fortification with ascorbic acid accelerated anthocyanin degradation in clarified juice at both storage temperatures, likely due to the loss of polymeric anthocyanin forms (21%) during clarification. Although clarification enhanced the amount of monomeric anthocyanins present in açai juice which relates positively to the aesthetic quality, processing and handling regimes must be optimized to achieve maximum retention of their functional properties during storage.     

Phenolic compounds in Chinese purple yam and changes during vacuum frying

Phenolic compounds and their changes during vacuum frying were investigated for a Chinese purple yam. Three cyanidin derivatives and one peonidin derivative were tentatively identified by HPLC–DAD–ESIMS analysis; sinapic acid and ferulic acid were identified by HPLC–DAD analysis with authentic chemicals. There were 31.0 mg/100 g (dry weight, DW) of total anthocyanin (ACN) and 478 mg/100 g DW of total phenolic content (TPC) in the fresh yam. Sinapic acid and ferulic acid were 135 and 31.3 mg/100 g DW respectively. The blanching process caused about 60% of ACN, and 30–50% of phenolic acids and TPC to be lost, which showed that anthocyanins were most vulnerable during blanching. The retention rate of the phenolic compounds during vacuum frying was 60–69%, indicating it was a practical technology for purple yam processing, on account of its impact on the phenolic compounds stability.     

澄清剂和温度对赤霞珠葡萄酒澄清效果的影响

为研究不同澄清剂和澄清温度对赤霞珠葡萄酒的澄清效果,本研究首先采用不同浓度梯度的皂土、明胶和海藻酸钠对2017年自酿赤霞珠葡萄酒进行澄清处理,以浊度、透光率、总酚含量和色度为评价指标,分别确定三种澄清剂的最佳使用量,筛选出两种澄清效果较好的澄清剂。此外,研究了筛选出的两种单一澄清剂(明胶:皂土)以1:1的配比组成的复合澄清剂,在不同温度(10、4、0和-4 ℃)下对赤霞珠葡萄酒澄清效果的影响,进而确定了赤霞珠葡萄酒澄清处理的最适温度。结果表明:单一澄清剂处理效果最佳的为明胶0.5 g/L,其次是皂土0.5 g/L、海藻酸钠0.25 g/L;复合澄清剂在4个温度处理条件下的澄清结果表明,前3 d的浊度、透光率、色度等各项指标随温度变化差异显著(p<0.05),5 d后趋于平稳,从处理7 d后的澄清指标与主要成分的变化来看,10 ℃处理澄清效果最佳,浊度为1.98 NTU,透光率96.60%,酒石酸1.32 g/L、多酚含量1105 mg/L和色度值1.09;4 ℃处理的效果次之,随着温度的降低(0 ℃和-4 ℃)其澄清效果逐渐降低,但各处理温度条件下各指标也有差异。因此,适宜的复合澄清剂(明胶:皂土=1:1)在10 ℃条件下对赤霞珠葡萄酒处理5~7 d可获得良好的澄清效果。     

Purification and identification of Capulin (Prunus serotina Ehrh) anthocyanins

Capulin (Prunus serotina Ehrh) anthocyanins were extracted from liquid nitrogen powdered epidermal tissue using acetone, the aqueous acetone extract partitioned with chloroform and purified in a C-18 solid-phase cartridge. pH-differential and bisulfite bleaching methods were used to determine monomeric anthocyanin content and polymeric color. Pigments were identified by spectral analyses, HPLC and mass spectroscopy. Information from HPLC profiles, saponification and acid hydrolysis of the capulin anthocyanins showed that the two major pigments were cyanidin-3-glucoside (34%) and cyanidin-3-rutinoside (63%), with no acylating groups. A third yellow/orange pigment (λ_max 480 nm, MW=632) possibly containing rutinose was detected by MS.     

Antioxidant activity, total phenolics content, anthocyanin, and color stability of isotonic model beverages colored with Andes berry (Rubus glaucus Benth) anthocyanin powder

The stability of anthocyanin (ACN) freeze-dried powders from Andes berry (Rubus glaucus Benth) as affected by storage, addition of maltodextrin as a carrier agent, and illumination was evaluated in isotonic model beverages. The ethanolic ACN extract was freeze dried with and without maltodextrin DE 20. Isotonic model beverages were colored with freeze-dried ACN powder (FDA), freeze-dried ACN powder with maltodextrin (MFDA), and red nr 40. Beverages were stored in the dark and under the effect of illumination. Half life of the ACNs, changes in color, total phenolics content (TPC), and antioxidant activity were analyzed for 71 d. Addition of maltodextrin and absence of light stabilized the color of beverages and improved ACN and TPC stability during storage. The antioxidant activity of the beverages was higher when they were colored with MFDA and highly correlated with ACN content. There was no correlation between antioxidant activity and TPC. It is concluded that addition of maltodextrin DE 20 as a carrier agent during freeze-drying improves the color and stability of nutraceutical antioxidants present in Andes berry extract. This suggests a protective enclosing of ACNs within a maltodextrin matrix with a resulting powder that could serve as a supplement or additive to naturally color and to enhance the antioxidant capacity of isotonic beverages.     

Color quality of Oregon strawberries--impact of genotype, composition, and processing

ABSTRACT:  This investigation was to evaluate fruit color and study the effect of processing on color quality of strawberry products. Three color instruments with different viewing angles, viewing areas, and sample presentation geometries were compared for their effectiveness in measuring CIE L *C* h ^o color values for fresh fruits of 6 strawberry genotypes. There were significant differences between genotypes as well as between instruments. Fruits from the Totem genotype were frozen, canned, and made into jam. Color changes were measured along with the following compositional determinations: total monomeric anthocyanins (ACN), total phenolic content (TPC), and percent polymeric color. ACN in fresh strawberries ranged from 37.1mg to 122.3 mg per 100 g of fresh fruit. Freezing resulted in an apparent increase in ACN and transfer of 70.2% of the anthocyanins from the berries into juice. Physical transfer of pigments to syrup also occurred with canning: there was approximately 70% loss in ACN, about 20% increase in polymeric color, and 23.5% decrease in TPC. Pronounced color change and substantial losses in ACN and TPC of strawberry jams occurred during processing and 9 wk of storage. Storage of jams at 38 °C compared to 21 °C over a period of 9 wk resulted in marked losses of ACN and TPC.     

Application of sepiolite in clarification of pomegranate juice: changes on quality characteristics during process

In this study, for the first time, the function of acid‐activated sepiolite clay was evaluated for clarification of pomegranate juice. The optimum conditions of clarification process were achieved using response surface methodology based on juice turbidity as a response. After that, under optimal condition, efficiency of sepiolite, bentonite and combination of these fining agents with gelatin and kieselgel was compared for clarifying pomegranate juice. The results showed that the best conditions for juice clarification were 0.05% (w/v) clay concentration, temperature of 50 °C and time of 2 h. The results revealed that treatments of bentonite–gelatin–kieselgel and sepiolite–gelatin–kieselgel were the most active fining agents that their use led to a reduction of 99.7% in turbidity of pomegranate juice. Kinetic study for different features was performed, and the results indicated that rate of changes in turbidity, viscosity, total phenolic contents and colour with time followed first‐, first‐, zero‐ and zero‐order kinetic models, respectively.     

脱色吸附剂对大豆脱色油返酸返色的影响

为对油脂精炼脱色加工提供参考,以活性白土、凹凸棒土以及二者复配作为脱色剂对大豆中和油进行脱色,测定脱色油的酸值、色泽,并通过返酸返色试验探究脱色吸附剂对大豆脱色油返酸返色的影响。结果表明：脱色油酸值与活性白土添加量和复配脱色剂中活性白土质量分数呈正相关,与凹凸棒土添加量呈负相关;脱色剂添加量越多,脱色效果越明显,但在活性白土或凹凸棒土添加量超过3%时,脱色效果增加较少;随活性白土或凹凸棒土添加量的增多,脱色油返酸总体呈先降后升趋势;脱色油会有不同程度的返色,与活性白土相比,凹凸棒土脱色返色程度更高。综上,在脱色过程中,通过调整脱色剂添加量和配比可在一定程度上控制成品油的返酸返色程度。