Fishy and hay-like off-flavours of dry spinach

 Gas chromatography-olfactometry of headspace samples revealed that (Z)-3-hexenal, methanethiol, (Z)-1,5-octadien-3-one, dimethyl trisulphide, octanal, 2-isopropyl- and 2-sec-butyl-3-methoxypyrazine are potent odorants of raw spinach. Boiling the spinach led to a change, such that dimethyl sulphide, methanethiol, dimethyl trisulphide, methional and 2-acetyl-1-pyrroline became the most important odorants. A further change was observed after drying and storage of raw spinach: methylpropanal, 2- and 3-methylbutanal and propanal were identified as the odorants with higher odour activity values. It was also found that (Z)-1,5-octadien-3-one and methional, in a concentration ratio of about 1 : 100, are responsible for the fishy off-flavour as dry spinach stored at lower temperatures under nitrogen. The hay-like flavour was caused by oxidative degradation of furan fatty acids, yielding 3-methyl-2,4-nonanedione. Received: 24 July 1997     

Fishy and hay-like off-flavours of dry spinach

 Gas chromatography-olfactometry of headspace samples revealed that (Z)-3-hexenal, methanethiol, (Z)-1,5-octadien-3-one, dimethyl trisulphide, octanal, 2-isopropyl- and 2-sec-butyl-3-methoxypyrazine are potent odorants of raw spinach. Boiling the spinach led to a change, such that dimethyl sulphide, methanethiol, dimethyl trisulphide, methional and 2-acetyl-1-pyrroline became the most important odorants. A further change was observed after drying and storage of raw spinach: methylpropanal, 2- and 3-methylbutanal and propanal were identified as the odorants with higher odour activity values. It was also found that (Z)-1,5-octadien-3-one and methional, in a concentration ratio of about 1 : 100, are responsible for the fishy off-flavour as dry spinach stored at lower temperatures under nitrogen. The hay-like flavour was caused by oxidative degradation of furan fatty acids, yielding 3-methyl-2,4-nonanedione. Received: 24 July 1997     

Characterisation of the key aroma compounds in a freshly reconstituted orange juice from concentrate

Application of an aroma extract dilution analysis on the entire volatile fraction isolated from an orange juice freshly reconstituted from concentrate revealed 40 odour-active constituents in the flavour dilution (FD) factor range of 4–2,048. Among them, ethyl butanoate and linalool showed the highest FD factor of 2,048, followed by octanal with an FD factor of 512. Thirty-six of the 40 odour-active compounds detected could be identified, all of which have previously been reported as volatile constituents of various orange juices. Quantification of 17 key odorants by stable isotope dilution assays followed by a calculation of odour activity values (OAVs) on the basis of odour thresholds in water or citrate buffer (pH 3.8), respectively, revealed the following most important odorants in the overall aroma of the freshly reconstituted juice: (R/S)-linalool, (R)-limonene and (S)-ethyl 2-methylbutanoate with the highest OAVs (>1,000) followed by octanal, (R)-α-pinene, ethyl butanoate, myrcene, acetaldehyde, decanal and (E)-β-damascenone with OAVs > 100. A model mixture containing all 14 aroma compounds with OAVs > 1 in their actual concentrations in the juice showed a good similarity with the aroma of the original orange juice under investigation, thus corroborating that the key odorants of a freshly reconstituted orange juice were characterised for the first time.     

Comparative study on shelf life of orange juice processed by high intensity pulsed electric fields or heat treatment

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,000 μs; bipolar 4-μs pulses at 200 Hz) on the microbial shelf life and quality-related parameters of orange juice were investigated during storage at 4 and 22 °C and compared to traditional heat pasteurization (90 °C for 1 min) and an unprocessed juice. HIPEF treatment ensured the microbiological stability of orange juice stored for 56 days under refrigeration but spoilage by naturally occurring microorganisms was detected within 30 days of storage at 22 °C. Pectin methyl esterase (PME) of HIPEF-treated orange juice was inactivated by 81.6% whereas heat pasteurization achieved a 100% inactivation. Peroxidase (POD) was destroyed more efficiently with HIPEF processing (100%) than with the thermal treatment (96%). HIPEF-treated orange juice retained better color than heat-pasteurized juice throughout storage but no differences (p<0.05) were found between treatments in pH, acidity and °Brix. Vitamin C retention was outstandingly higher in orange juice processed by HIPEF fitting recommended daily intake standards throughout 56 days storage at 4 °C, whereas heat-processed juice exhibited a poor vitamin C retention beyond 14 days storage (25.2–42.8%). The antioxidant capacity of both treated and untreated orange juice decreased slightly during storage. Heat treatments resulted in lower free-radical scavenging values but no differences (p<0.05) were found between HIPEF-processed and unprocessed orange juice.     

Flavour and off-flavour compounds of black and white pepper (Piper nigrum L.) III. Desirable and undesirable odorants of white pepper

 Quantification of 19 odorants and calculation of their odour activity values were together the basis for an aroma model which reflected the odour profile of a white pepper sample having a faecal off-flavour. Omission tests indicated limonene, linalool, α-pinene, 1,8-cineole, piperonal, butyric acid, 3-methylbutyric acid, methylpropanal, and 2- and 3-methylbutanal as key odorants of white pepper. The faecal off-flavour was caused by skatole and was enhanced by the presence of p-cresol. In six samples of white pepper the intensity of the faecal off-flavour paralleled the concentration of both skatole and p-cresol. In the sample with the strongest off-flavour the concentrations amounted to 2.6 mg/kg (skatole) and 12.4 mg/kg (p-cresol).     

Formation of α-terpineol in Citrus Juices, Model and Buffer Solutions

The formation of α-terpineol from its putative precursors in citrus juice (d-limonene and linalool) was investigated in juice, buffers and model solutions. α-Terpineol content was higher in commercial lemon juice than in orange or grapefruit juices. Its content exceeded its taste threshold of 2.5 mg/L in orange juice stored for 1 month at 35 °C. During storage of homogenized model solutions fortified with d-limonene or linalool, α-terpineol was simultaneously formed and degraded, especially at 45 °C and its formation was strongly dependent on pH. Linalool was a more reactive substrate than limonene for α-terpineol formation; the protonation in linalool was faster than in limonene. However, since there was more limonene than linalool in citrus juices, a-terpineol appeared to have been formed to about the same extent from both precursors.     

Limonene, linalool, α-terpineol, and terpinen-4-ol as quality control parameters in mandarin juice processing

Consumers demand commercial citrus juices resembling fresh juices; however, citrus juice elaboration is quite delicate due to the formation of off-flavors during heat treatment and storage. Four volatile compounds, d-limonene, linalool, α-terpineol, and terpinen-4-ol were extracted using the dynamic headspace technique and were identified and quantified by GC-MS in mandarin juices from two Spanish varieties, Fortuna and Clemenules. Our results clearly demonstrated that both the pasteurization and storage steps significantly affected concentrations of these four aroma compounds. Formation of off-flavors components, α-terpineol and terpinen-4-ol, and simultaneous decomposition of d-limonene and linalool were observed in mandarin juices. Therefore, measurements of the stability of d-limonene and linalool, and formation of α-terpineol and terpinen-4-ol will help mandarin juice producers in analyzing the quality of their products.     

Hay-like off-flavour of dry parsley

 The flavour of parsley was found to change during drying and storage. Quantification of 27 potent odorants, selected by dilution experiments and calculation of odour activity values, indicated that 3-methyl-2,4-nonanedione was mainly responsible for the hay-like off-flavour. Two furanoid fatty acids, known to be precursors of 3-methyl-2,4-nonanedione, were detected in dry parsley. The decrease in the intensities of the parsley-like, metallic and green notes in the odour profile during storage of dry parsley was due to losses of p-mentha-1,3,8-triene, myrcene and (Z)-6-decenal. Sulphurous cabbage-like and malty notes were caused by dimethyl sulphide, methylpropanal as well as 2- and 3-methylbutanal. The effect of the water activity (at a _w levels of 0.15, 0.25, 0.35) on the changes in the concentrations of all these compounds during storage of dry parsley was investigated. Received: 24 July 1997     

Spray drying conditions for orange juice incorporated with lactic acid bacteria

This work aimed to develop an orange juice powder by spray drying with lactic acid bacteria (Lactobacillus plantarum 299v and Pediococcus acidilactici HA‐6111‐2), testing their survival both during drying and storage (room temperature and 4 °C). Initially, the best conditions for spray drying were chosen to allow the best survival of each LAB: (i) inlet air temperature of 120 °C and (ii) 0.5:2 ratio of the orange juice soluble solids and drying agent added (prebiotics: 10 DE maltodextrin or gum Arabic). Survival of LAB was not affected by drying process, and it was higher when cultures were stored at 4 °C. A slightly higher protection was conferred by 10 DE maltodextrin, in the case of L. plantarum and at 4 °C. Pediococcus acidilactici was more resistant during storage at 4 °C, with logarithmic reductions lower than 1 log‐unit. It was demonstrated that it is possible to produce a functional nondairy product, orange juice powder supplemented with prebiotic compounds, containing viable LAB for at least 7 months, when stored at 4 °C.     

Thermal processing,storage conditions,and the composition and physical properties of orange juice

Mexican orange juice bottled without pasteurization and frozen, or orange juice that was pasteurized, bottled, and frozen or orange juice pasteurized and stored at 1°C in plastic bins was sampled monthly for eight months. Juice density, cloud, and fructose levels were all significantly (P<0.05) affected by the method of processing. Pasteurization reduced orange juice ascorbic acid concentrations. The concentrations of acetaldehyde and ethyl acetate were highest in unpasteurized juice. α-pinene, β-myrcene, limonene, α-terpineol, 1-hexanol, 3-hexen-1-ol and sabinene concentrations were highest in the unpasteurized juice.     

Investigation of citrus flavor adsorption during debittering of grapefruit juice using kinetic modeling and response surface methodology

Reconstituted grapefruit juice was debittered with XAD-7HP adsorbent resin in batch experiments and the adsorption rate constants of the bitter principal naringin and the volatile flavor compounds α-pinene, β-myrcene, dlimonene, α-terpineol, and β-caryophyllene were determined using a pseudo-first order kinetic model. The highest rate constants were observed consistently for the off-flavor α-terpineol, followed by naringin and the other flavor compounds. The rate constant of each substance was influenced significantly by temperature, ratio of adsorbent/juice, and, except for α-terpineol, by the interaction of both factors (p<0.05). Response surface methodology (RSM) was applied for the development of regression models to predict the adsorption rate constants of all substances. On the basis of the regression models for d-limonene and naringin, a factor combination that minimized loss of flavor and maximized bitterness reduction during the debittering procedure was determined to be a combination of low temperature (13.9°C) and high adsorbent/juice ratio (3.6%).     

贮藏过程中夏橙汁香气成分变化

为探明贮藏对夏橙汁香气成分的影响,通过冷藏(5℃)、室温、加速贮藏(30、40、50℃)灭菌夏橙汁,分别于2、4、6周取样,采用固相微萃取-气相色谱-质谱法分析香气成分,内标法半定量。结果表明：夏橙汁在贮藏过程中,柠檬烯、β-月桂烯、芳樟醇、辛醛、癸醛、丁酸乙酯等对香气有重要贡献的成分的含量有所下降;冷藏6周后各类成分含量下降缓慢,加速贮藏6周后烯烃类下降显著,但醇类、酮类及酯类等总含量下降不显著;α-松油醇、β-松油醇、糠醛、4-乙烯基愈创木酚等对橙汁品质有反作用的成分较对照组均有增加。故要保持夏橙汁固有的香气,应严格控制贮藏温度,其中以冷藏条件为最佳。     

Identification of Spoilage Marker Metabolites in Irish Chicken Breast Muscle Using HPLC,GC–MS Coupled with SPME and Traditional Chemical Techniques

The aim of this investigation was to determine the metabolites of spoilage present on the surface of Irish chicken breast muscle in order to identify biomarkers of microbial spoilage and to verify the results of a previous study which suggested that the increase of free amino acids is the main spectral influence factor leading to the near and middle infrared detection of microbial spoilage. Irish-reared chicken breast muscle samples were individually packed and stored at 4 °C for 8 days under aerobic conditions. Microbiological analysis revealed that Pseudomonas spp. and Brochothrix thermosphacta were the predominant organisms (total viable counts (TVC), 4.24, 6.37 and 8.6 colony forming unity (CFU) g⁻¹ for days 0, 4 and 8, respectively, Pseudomonas 3.2, 5.1 and finally, on day 8 7.4 log CFU g⁻¹). Glucose and L-lactate concentrations decreased but the concentration of water-soluble polypeptides and amino acids increased over storage time. HPLC analysis of free amino acids revealed an increase of the total concentration but the composition of the profiles did not change over time. Headspace analysis detected the following volatile compounds: ethanol, acetone, ethyl acetate, methyl benzoate, heptane, C15, C12, methyl ethyl ketone, carbon disulphide, dimethyl sulphide, hexanal, and toluene. Of interest is the fact that detection of sulphides and an increase of ethanol, acetone, and ethyl acetate concentrations occurred from day 4 to 8. The increase in free amino acids throughout storage and the production of volatile compounds after day 4 require further investigation but are selected as potential biomarkers of microbial spoilage as they could be analytically detected before the accepted levels of sensory spoilage detection.     

Flavor Evaluation and Volatile Flavor Constituents of Stored Aseptically Packaged Orange Juice

Samples of commercial orange juice packaged aseptically and stored at 21°C and 26°C were evaluated weekly by a sensory panel using hedonic ratings. Flavor scores were significantly lower than control juice and unacceptable after 1 wk at 26°C and 2 wk at 21°C. The flavor score decreased to 50–60% of the starting value during 6 wk storage. The volatile components, α-terpineol and ethyl acetate, increased during storage. A component not identified earlier as a volatile citrus component was identified as 2-(2-butoxyethoxy)ethanol. This and the observed increase in ethyl acetate during storage might have come from the laminated multilayered package liner. Limonene in juice decreased about 40% during storage. Other major volatile components did not change markedly.     

Orange juices enriched with chitosan: Optimisation for extending the shelf-life

Optimisation of the incorporation of chitosan in orange juice was accomplished by the evaluation of quality and nutritional markers. Response surface methodology was applied to obtain quadratic and second degree response surface model equations. The analyses showed that increases in chitosan concentration extended the quality of the orange juice significantly (p < 0.05), reducing enzymatic and non-enzymatic browning and controlling the spoilage during the storage time; however, concentrations > 1 g L^− 1 produced a significant (p > 0.05) reduction in the concentrations of ascorbic acid and carotenoids associated with the positive charge of chitosan and its ability to flocculate and coagulate negatively charged substances. Also, concentrations > 1 g L^− 1 were scored as unacceptable for the sensory panel due to an increase in bitterness. The study recommends the use of chitosan at concentrations up to 1 g L^− 1 to extend quality and preserve ascorbic acid and carotenoids during storage time of fresh orange juice, thus avoiding the use of standard thermal treatments which produces a negative impact on the nutritional value.

Industrial relevance

One of the major problems of fresh orange juice is its limited shelf-life. Spoilage and quick degradation of vitamins are two of the most important causes of quality loss during the shelf-life of this product. Moreover, the U. S. Food and Drug Administration issued a warning to consumers against drinking unpasteurised orange juice products because of the potential contamination with Salmonella typhimurium and its association with an outbreak of human disease caused by this organism [FDA issues nationwide health alert on Orchid Island unpasteurised orange juice. Products Recalls, Market Withdrawals and Safety Alerts.]. The main objective of this study was the study of chitosan as a natural preservative for extending the shelf-life of orange juice and as an alternative to pasteurisation.     

On the non-enzymatic liberation of limonin and C17-epilimonin from limonin-17-β-d-glucopyranoside in orange juice

Limonin is well-known to induce the so-called “delayed” bitterness which is developing during standing and/or processing of orange juice. The objective of this study was to investigate the hydrolytic liberation of limonin from its precursor limonin-17-β-d-glucopyranoside in aqueous model solutions and orange juice samples. Quantitative model studies on the degradation of limonin-17-β-d-glucopyranoside under acidic conditions as well as during storage of orange juice revealed the formation of limonin besides a second hydrolysis product of yet unknown structure. After isolation, the structure of that compound was unequivocally determined for the first time as the C₁₇-epimer of limonin, named C₁₇-epilimonin. In order to investigate the generation of these triterpenoid lactones during storage as well as heat-treatment of orange juice, freshly squeezed orange juice was stored for up to 4 weeks at 4 and 20 °C or was heated at 70 and 100 °C and, then, both limonoids were quantitatively determined by means of high performance liquid chromatography-mass spectrometry/mass spectrometry (multiple reaction monitoring). The data obtained showed first evidence for the use of the C₁₇-epilimonin/limonin ratio as a suitable marker for the analytical determination of the thermal input applied during processing orange juice products.     

Flavour and off-flavour compounds of black and white pepper (Piper nigrum L.) I. Evaluation of potent odorants of black pepper by dilution and concentration techniques

 Dilution and concentration experiments as well as enantioselective analysis of optically active monoterpenes indicated (±)-linalool, (+)-α-phellandrene, (–)-limonene, myrcene, (–)-α-pinene, 3-methylbutanal and methylpropanal as the most potent odorants of black pepper. Additionally, 2-isopropyl-3-methoxypyrazine and 2,3-diethyl-5-methylpyrazine were detected as important odorants of a black pepper sample with a mouldy, musty off-flavour. Received: 24 September 1998     

Stability of anthocyanins and ascorbic acid in sonicated strawberry juice during storage

The stability of anthocyanins and ascorbic acid in sonicated strawberry juice during storage was investigated. Strawberry juice was sonicated at varying acoustic energy densities (AEDs) ranging from 0.33 to 0.81 W/mL and treatment times of 0–10 min. The degradation kinetics of sonicated samples followed first-order kinetics. Degradation rate constants were linearly correlated with AED (R ² > 0.91). Selected samples were stored for 10 days at 4 and 20 °C. A second-order polynomial model was employed to investigate the effects of storage time and processing variables. During storage higher loses were observed at a storage temperature of 20 °C compared to 4 °C. Predictive models developed for anthocyanins and ascorbic acid content were highly significant (P < 0.0001) and closely correlated to the experimental data (R ² > 0.91). Degradation mechanisms for anthocyanins and ascorbic acid due to sonication and storage are proposed.     

Effect of refrigerated storage on ascorbic acid content of orange juice treated by pulsed electric fields and thermal pasteurization

Application of pulsed electric fields (PEF) can lead to longer shelf life of fruit juices with minimal product quality loss and good retention of fresh-like flavour. The aim of this study was to evaluate the effect of PEF and conventional pasteurization (90 °C, 20 s) on ascorbic acid content of orange juice, and to assess modifications in ascorbic acid concentration of orange juice stored in refrigeration at 2 and 10 °C for 7 weeks. The ascorbic acid degradation rate was −0.0003, −0.0006, −0.0009 and −0.0010 μs⁻¹ for fields of 25, 30, 35 and 40 kV/cm, respectively. With selected PEF treatment (30 kV/cm and 100 μs) the shelf life based on 50% ascorbic acid losses was 277 days for the PEF-treated orange juice stored at 2 °C, while for the pasteurized juice was 90 days.     

Study of chemical changes in pasteurised orange juice during shelf-life: A fingerprinting-kinetics evaluation of the volatile fraction

The current work used fingerprinting-kinetics for the first time to monitor shelf-life changes in a low-pH, pasteurised, shelf-stable product, more particular in orange juice. Orange juice samples were stored as a function of time at four different storage temperatures (20, 28, 35 and 42 °C). To obtain insight into chemical changes in the volatile food fraction, samples were fingerprinted with headspace GC–MS. The objectives of this work were twofold: (i) to identify major chemical changes of pasteurised orange juice during shelf-life and (ii) to study the kinetics of selected shelf-life compounds in the context of accelerated shelf-life testing (ASLT). At 20 °C, changes in terpenes and a decrease in aldehydes were observed. Oxides and sulphur compounds increased and esters decreased at increased storage temperatures (at 28 °C and above). Concerning ASLT, four volatile compounds had clear temperature and time dependent kinetics within the investigated temperature range.