Mehmet Özkan

Effects of various pressing programs and yields on the antioxidant activity, antimicrobial activity, phenolic content and colour of pomegranate juices

Pomegranate juice (PJ) samples were produced with three different pressing programs: (1) 1.2-4.8 bar for 25 min, (2) 1.2-2.4 bar for 15 min and (3) 1.2-1.8 bar for 5.5 min. Respective juice yields were 39.2%, 33.2% and 27.2%. Effects of pressing pressure-time and yield on total phenolic (TP) content, condensed tannin (CT) content, monomeric anthocyanin (MA) content, antioxidant activity (AOA) and antimicrobial activity (AMA) of the samples were determined. Strong positive linear correlations were found between the pressing pressure with AOA (r=0.973) and TP content (r=0.979), while negative logarithmic correlations were found between pressing pressure with the contents of CT (r=-0.778) and MA (r=-0.955). Among 12 microorganisms tested, Bacillus megaterium, Bacillus subtilis, Staphyloccocus aureus and Pseudomonas sp. were found to be sensitive to juice samples. However, increasing pressing pressure and yield did not lead to a significant change on the AMAs of the juices.

Clarification and pasteurisation effects on monomeric anthocyanins and percent polymeric colour of black carrot (Daucus carota L.) juice

Black carrots (BCs) are a rich source of stable anthocyanins (ACNs). The purpose of this study was to evaluate the effects of clarification and pasteurisation on ACNs of black carrot juice (BCJ). Monomeric ACNs, ACN profile and percent polymeric colour were determined during processing of BCJ. While depectinisation and bentonite treatments resulted in 7% and 20% increases in monomeric ACN content of BCJ, respectively, gelatine-kieselsol treatment and pasteurisation resulted in 10% and 3-16% reduction. Percent polymeric colour decreased after clarification, but substantially increased in samples subjected to heat. ACNs of BCJ samples were identified by HPLC-MS. Unclarified BCJ contained cyanidin-3-galactoside-xyloside-glucoside-ferulic acid as the major ACN, followed by cyanidin-3-galactoside-xyloside-glucoside-coumaric acid, and cyanidin-3-galactoside-xyloside-glucoside. After depectinisation, two more ACNs (cyanidin-3-galactoside-xyloside and cyanidin-3-galactoside-xyloside-glucoside-sinapic acid) were also identified. These results indicated that depectinisation and bentonite treatment had positive effect on the colour of BCJ, while gelatin-kieselsol treatment and pasteurisation had negative effect.

Colour stabilities of sour cherry juice concentrates enhanced with gallic acid and various plant extracts during storage.

Gallic acid (GA) and pomegranate rind extract (PRE), cherry stem extract (CSE) and green tea extract (GTE) were added to sour cherry juice concentrates (SCJCs) to enhance the colour. Effects of these copigment sources on anthocyanins, colour and turbidity were investigated during storage at -20, 4 and 20°C for 110 days. Cyanidin-3-glucosylrutinoside (cyd-3-glu-rut, 75%) was the major anthocyanin, followed by cyanidin-3-rutinoside (cyd-3-rut, 23%) and cyanidin-3-sophoroside (cyd-3-soph, 2%). While GA (37-53%), PRE (27-77%) and GTE (44-119%) increased the stabilities of cyd-3-rut and cyd-3-glu-rut, CSE reduced (12-24%) the stabilities of all anthocyanins. Polymeric colour and turbidity values increased after the addition of all extracts and GA. The lowest turbidity value after 110 days of storage at 20°C was determined in the SCJC enhanced with PRE. We recommend the addition of PRE to SCJC for the enhancement of anthocyanin stability and colour intensity, and the reduction in turbidity.

Loss of sulfur dioxide and changes in some chemical properties of Malatya apricots (Prunus armeniaca L.) during sulfuring and drying

BACKGROUND This study was conducted to determine the differences in some analytical properties of four apricot cultivars and to determine the changes in these analytical properties during sulfuring and sun-drying. RESULTS There were significant differences in the contents of polyphenols, carotenoids and organic acids (OA) as well as antioxidant activities (AOAs) of the cultivars (P < 0.05). After sulfuring and drying, considerable reductions were detected in the contents of total polyphenols (TPCs, 11-26%), OAs (4-32%) and β-carotene (6-21%), and AOAs (2-21%) of the samples. Sun-drying resulted in 71-83% decreases in sulfur dioxide (SO2 ) contents of sulfured-dried apricots (SDAs) in comparison with apricots immediately after sulfuring. As the TPCs increased, the SO2 absorption by the samples also increased. In contrast, the OA contents had no effect on SO2 absorption, but an increase in OA content resulted in an increase in the browning values of the SDAs. As expected, increases in contents of ferulic acid (r = 0.932), chlorogenic acid (r = 0.850), epicatechin (r = 0.804) and quercetin (r = 0.750) led to an increase in browning values of the SDAs. CONCLUSION There were significant effects of cultivar and processing on the physico-chemical properties investigated in the study, and with the absorption of SO2 and the formation of a brown colour in the samples.

Effects of sulfur dioxide concentration on organic acids and β-carotene in dried apricots during storage

The effects of various sulfur dioxide (SO2) concentrations (0, 451, 832, 1594, 2112 and 3241mg/kg) on the profiles and contents of organic acids (OAs) and β-carotene in sulfured dried apricots (SDAs) were investigated during storage at 4, 20 and 30°C for 379days. In all samples, four OAs [malic acid (MA), citric acid (CA), succinic acid (SA) and oxalic acid (OXA)] were identified. SA (13.9-31.8g/kgdw) was the major OA in SDAs containing SO2 at lower than 1594mgSO2/kg, while MA (11.7-11.7g/kgdw) was the major OA in SDAs containing SO2 at higher than 1594mgSO2/kg. As SO2 concentration increased, CA and OXA contents increased whereas MA contents decreased. Moreover, the highest stabilities of β-carotene, MA and SO2 were determined in SDAs containing 1594mgSO2/kg at 4°C. Therefore, we suggest using 1594mgSO2/kg and storing SDAs at 4°C to protect OAs and β-carotene.

Effects of various protein- and polysaccharide-based clarification agents on antioxidative compounds and colour of pomegranate juice.

The effects of natural sedimentation and clarification agents [protein-based (albumin, casein and gelatin) and polysaccharide-based (chitosan and xanthan gum)] on total phenolics, hydrolysable tannins, anthocyanins and antioxidant activity of pomegranate juice were investigated. While protein-based agents led to higher reductions in the contents of total phenolics (7.2-17.2%), hydrolysable tannins (16.7-59.5%) and anthocyanins (11.7-23.7%) (p<0.05) than natural sedimentation, polysaccharide-based agents had similar effects on these compounds, like natural sedimentation (p>0.05). The stabilities of β-punicalagin and α-punicalagin (the major hydrolysable tannins) against clarification were similar. Moreover, antioxidant activities of the samples clarified with polysaccharide-based agents were higher (2.4-26.6%) than those of the protein-based agents. For both high total phenolic, hydrolysable tannin and anthocyanins contents, as well as high antioxidant activity, we suggest that polysaccharide-based agents be used for the clarification of pomegranate juice. In fact, chitosan is especially recommended for this purpose since chitosan (10.3NTU) led to lower turbidity as compared to xanthan gum (20.0 NTU).

Effects of condensed tannins on anthocyanins and colour of authentic pomegranate (Punica granatum L.) juices

This study was conducted to determine the effects of condensed tannins (CT) on anthocyanins (ACNs) and colour of pomegranate juice (PJ) samples obtained from nine registered varieties in Turkey. CT-catechins (CTCs) reactive to vanillin and phloroglucinol adducts of CT contents were determined. CTC and ACN contents of PJs highly depended on variety (p<0.01), and ranged from 31 to 155 mg/L juice and from 47 to 405 mg/L juice, respectively. As catechin-phloroglucinol content increased, ACN content also increased (r=0.866). Strong logarithmic correlation between the ratio of ACN contents to catechin-phloroglucinol contents and polymeric colour (PC) values of the samples was found (r=-0.822). When PC value of PJs was ⩾8% or ratio of ACN contents to catechin-phloroglucinol contents of PJs was ⩽2.82, ACN contents of the samples determined by spectrophotometric method were higher than those determined by HPLC.

Effect of SO2 on sugars, indicators of Maillard reaction, and browning in dried apricots during storage

BACKGROUND The effect of sulfur dioxide (SO2 ) concentration was determined on sugars and indicators in the Maillard reaction (MR), and on browning, in sulfured, dried apricots (SDAs) during storage at 4, 20 and 30 °C for 379 days. RESULTS As SO2 concentration increased, the content of reducing sugars involved in the MR also increased. The preventive effect of SO2 on the MR could not result from the binding of SO2 to reducing sugars. Before storage, furosine was detected in the non-SDAs but 5-hydroxymethylfurfural (HMF) was not detected. Even the lowest SO2 concentration (451 mg kg-1 ) was sufficient to prevent the formation of furosine and HMF during drying of apricots. CONCLUSION Formation of furosine and HMF in all samples during storage at 20 and 30 °C for 379 days indicated that SO2 could not prevent the first and intermediate stages of MR in SDAs during storage. Thus, the main prevention effect of SO2 on browning in SDAs occurred during drying, not storage.

Changes in polyphenol profile of dried apricots containing SO2 at various concentrations during storage

BACKGROUND Changes in polyphenols have important effects on the quality (especially color) and health benefits of dried apricots. SO2 concentration, storage and the activities of polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were factors which had significant effects on polyphenols. Polyphenol profile and activities of PPO and PAL in sulfured dried apricots (SDAs, 0, 451, 832, 2112 and 3241 mg SO2 kg-1 ) were monitored during storage at 4, 20 and 30 °C for 379 days for the first time. RESULTS Even the lowest SO2 concentration (451 mg kg-1 ) was sufficient to inactivate PPO during the entire storage period. However, while SO2 led to the increase in PAL activity of the samples (r = 0.767) before storage, PAL activities of SDAs decreased during storage. After 90 days of storage, PAL activity was determined in only non-sulfured dried apricots (NSDAs) and dried apricots containing 451 mg SO2 kg-1 . Although the major polyphenol in NSDAs was epicatechin (611.4 mg kg-1 ), that in SDAs was chlorogenic acid (455-1508 mg kg-1 ), followed by epicatechin (0-426.8 mg kg-1 ), rutin (148.9-477.3 mg kg-1 ), ferulic acid (23.3-55.3 mg kg-1 ) and gallic acid (2.4-43.6 mg kg-1 ). After storage at 30 °C for 379 days, the major polyphenol in SDAs was gallic acid (706-2324 mg kg-1 ). However, the major polyphenol in NSDAs did not change after storage. The highest total polyphenol content was detected in SDAs containing 2112 mg SO2 kg-1 and stored at 30 °C. CONCLUSION To produce dried apricots having high polyphenol content, ∼2000 mg SO2 kg-1 should be used. Low storage temperature (<30 °C) was not necessary for the protection of polyphenols.

Narın Farklı Bölümlerinin Polifenol İçeriği, Antioksidan ve Antibakteriyel Aktivitesi Üzerine Ekstraksiyon Çözgenlerinin Etkisi

Nar kabugu, dilim zari ve cekirdeklerinde bulunan polifenoller; aseton, aseton:su ( 70:30, v:v), metanol, etanol ve su ile 4 ° C’de 24 saat suresince ekstrakte edilmistir. Nar kabugu ve dilim zarinda; gallik asit, punikalin, a -punikalajin, b -punikalajin ve ellajik asit turevleri HPLC ile tanimlanirken, cekirdekte sadece elajik asit turevleri tanimlanmistir. Nar kabugu ve dilim zarinin cok yuksek miktarda polifenol icerdigi belirlenmistir. Nar kabugu (r=0.967), dilim zari (r=0.976) ve cekirdeklerden (r=0.972) elde edilen ekstraktlarin toplam polifenol miktari ve antioksidan aktiviteleri arasinda guclu korelasyonlar bulunmustur. Ayrica, en yuksek toplam polifenol madde miktari ve antioksidan aktivite aseton:su (70:30, v:v) cozeltisiyle elde edilmistir. Nar kabugu ve dilim zarinin yuksek antioksidan ve antibakteriyel aktivitesi punikalajinlerden kaynaklanmaktadir. Nar kabugu ve dilim zari Bacillus megaterium and Staphylococcus aureus’a karsi antibakteriyel aktivite gostermistir. Yuksek antioksidan ve antibakteriyel aktiviteleri nedeniyle, nar kabugu ve dilim zarinin sulu ekstraktlari gida katkisi ve koruyucusu olarak kullanilabilir.