Effects of some technological processes on glucosinolate contents in cruciferous vegetables

Effects of blanching, boiling and freezing of selected cruciferous vegetables (Brussels sprouts, white and green cauliflower, broccoli, and curly cale) on their glucosinolate (GLS) contents were determined. It was found that blanching and cooking of the vegetables led to considerable (P < 0.05) losses of total GLS, from 2.7 to 30.0% and from 35.3 to 72.4%, respectively. No systematic changes in total GLS were found in the vegetables that were blanched and frozen for 48 h. In addition, the highest concentration of cancer-protective compounds, such as aliphatic and indole GLS, were found in Brussels sprouts (sinigrin and glucobrassicin) and in broccoli (glucoraphanin).     

Effects of traditional and modified technology,in the production of frozen cauliflower,on the contents of selected antioxidative compounds

The investigation concerned white and green cauliflowers: a traditional technology of freeze – blanched cauliflower, a modified technology of freeze – cooked cauliflower, and two temperatures of frozen storage at −20 and −30 °C for 0, 4, 8, and 12 months. Compared with the white cauliflower, the green variety was characterized by significantly greater contents of dry matter, vitamin C, carotenoids, β-carotene, polyphenols and a higher antioxidative activity at all the stages of evaluation. Depending on the investigated sample, after 12 months of refrigerated storage, cauliflower prepared for consumption retained 29–50% of vitamin C, 73–100% of carotenoids, 53–125% of β-carotene, 69–85% of polyphenols and 26–40% of antioxidative activity in comparison with the raw material. After a 12-month storage, the product obtained using the modified technology contained significantly more vitamin C and in general showed a higher antioxidative activity than did with the traditional product. The lower storage temperature resulted in significantly better retention of vitamin C and also – in some samples – a better retention of carotenoids, β-carotene, and polyphenols. A higher sensory quality was found in products of green cauliflower obtained according to the traditional technology.     

Evaluation of the amino acid content and sensory value of flageolet bean seeds (Phaseolus vulgaris L.) as affected by preprocessing methods before freezing

The aim of the work was to evaluate the content of amino acids in flageolet bean seeds, prepared for consumption from frozen products obtained using different methods. One of the frozen products was obtained using the traditional method (blanching–freezing–frozen storage) and then cooked. The other was obtained using the modified technology (cooking–freezing–frozen storage), followed by defrosting and heating in a microwave oven. The culinary and technological processing applied brought about a pronounced decrease in tyrosine content (35–47% in 16 g N). The content of the remaining amino acids decreased or increased in relation to the raw material within the extremes of ?15% to +17%. Sulphur amino acid was the limiting amino acid. Product obtained using traditional method had the higher quality protein (EAA index 144–166) of seeds prepared for consumption. In sensory test products, blanched before freezing were evaluated a bit higher than those cooked before freezing (ready‐to‐eat).     

EFFECT OF BLANCHING AND SULFITE TREATMENT ON THE QUALITY OF FROZEN CAULIFLOWER

The influence of blanching time and post-blanching sulfite treatment on the sensory quality and texture of frozen cauliflower were assessed after storage at -18°C for up to one year. The treated cauliflower florets, sealed in polyethylene bags, were placed in waxed paperboard cartons and frozen in a contact plate freezer at -35°C. Samples blanched for 3 min and dipped in a solution containing 1000ppm of SO₂ for 5 min gave a significantly (p<0.05) superior product even when stored for one year. The residual SO₂ content of 50 ppm found in these stored samples disappeared after a 3 min cooking in boiling water. Cauliflower texture was influenced by blanching time but the textural differences of blanched samples diminished following freezing and storage. After a 3 min cooking, the texture of all thawed samples were comparable to that of fresh cauliflower cooked for 10–12 min.     

A comparative study on the polyphenolic content,antibacterial activity and antioxidant capacity of different solvent extracts of Brassica oleracea vegetables

Brassica vegetables are rich in polyphenols, flavonoids and glucosinolates. Investigation was undertaken to optimise the best solvents among 60% ethanol, acetone and methanol for the extraction of polyphenols from Brassica vegetables. Furthermore, different properties such as antibacterial activity and antioxidant capacity were also investigated. Results showed that a 60% methanolic extract showed the highest total phenolic content which was 23.6, 20.4 and 18.7 mg gallic acid equivalents (GAE) g^?1 extract for broccoli, Brussels sprouts and white cabbage, respectively. The hydroxybenzoic acid content of various solvent extracts ranged from 5.86 to 8.91 GAE g^?1 extract for broccoli, 2.70 to 5.44 GAE g^?1 extract for Brussels sprouts and 3.69 to 4.86 GAE g^?1 extract for white cabbage, while the hydroxycinnamic acid content ranged from 0.78 to 1.26 chlorogenic acid equivalents (CAE) g^?1 extract for broccoli, 1.41 to 3.45 CAE g^?1 extract for Brussels sprouts and 0.49 to 1.14 CAE g^?1 extract for white cabbage. A concentration‐dependent antioxidative capacity was confirmed for different reactive oxygen species, and moderate antibacterial activity was observed against a number of Gram‐negative and Gram‐positive food spoilage and food pathogenic bacteria. Solvents significantly affected polyphenolic content and its different properties, and the methanol was found to be the best solvent for the extraction of polyphenols from studied Brassica vegetables.     

Kinetic Parameters for the Thermal Inactivation of Peroxidase and Lipoxygenase in Precooked Frozen Brassica Species

Thermal inactivation of peroxidase (POD) and lipoxygenase (LOX), both enzymes present in broccoli and Brussels sprouts, is required before freezing, to obtain high‐quality precooked frozen vegetables. Rate constants of a 1st‐order biphasic model for the heat‐labile and heat‐resistant POD and LOX isoenzymes were determined at different temperatures (75, 80, and 90 °C) and the corresponding activation energies were estimated using nonlinear regressions. In the case of Brussels sprouts, the activation energies for the resistant and labile fractions were 56.3 and 62.5 kJ/mol for POD and 63.7 and 65.8 kJ/mol for LOX, respectively. For Brussels sprouts, different precooking times were tested to analyze the effect of residual enzyme activity on quality parameters and sensory attributes, after a frozen storage of 4 mo at ?20 °C. A significant reactivation of enzyme activity after frozen storage was observed (especially in the case of POD) for short precooking times (<6 min) leading to low‐quality parameters at the interior zone of the vegetable. A precooking time of 6 min at 90 °C allowed an adequate inactivation of LOX and POD obtaining a high‐quality final frozen vegetable. A sensory analysis confirmed the global acceptability of the product. The obtained results are relevant to define the precooking stage conditions in the production of frozen cruciferous vegetables.     

An estimate of the mean daily intake of glucosinolates from cruciferous vegetables in the UK

Samples (174) of cabbage, Brussels sprouts, cauliflower and swede-turnip have been analysed for total and individual glucosinolate content in both the fresh and cooked form. Using data from the 1980 National Food Survey, the national mean daily intake is calculated to be 46.1 mg in fresh material, and 29.4 mg in cooked. There are large variations within the UK (for example in Scotland it is less than half that in south-west of England), between income groups and over the year. National mean daily intake figures for the glucosinolates yielding goitrogenic products such as oxazolidine-2-thiones and thiocyanate ion are 6.7 and 14.7 mg respectively; the former figure is approximately doubled in the winter months. Based upon the above variations, arising from eating habits in the UK, together with the known large variation in glucosinolate content in cruciferous plants because of agronomic and environmental effects, it is likely that certain individuals will consume more than 300 mg total glucosinolates per day. The nutritional and toxicological consequences of such an intake are unknown at present.     

Potential of Near Infrared Reflectance (NIR) Spectroscopy for Estimating Nutrient Content of Dehydrated Vegetables

A near infrared reflectance (NIR) spectrophotometric procedure was evaluated for potential use in assaying nutrient contents of vegetables. Dried ground samples of cauliflower, broccoli, Brussels sprouts, spinach, asparagus, peas, green beans, and squash were analyzed chemically for crude protein, crude fat, ash, and neutral detergent fiber (NDF) and then scanned to develop NIR prediction equations. For the 75 calibration foods samples, the respective correlation coefficients between actual and NIR predicted values of these food components were 0.97, 0.77, 0.91, 0.81. Predictions for 26 unknown samples, which included cabbage, carrots, chard, corn, onions and rhubarb, were based on NIR equations developed from the first 75 samples. The resultant correlations were 0.95, 0.49, 0.85, and 0.78, respectively, for crude protein, crude fat, ash and NDF. NIR prediction detected incorrect chemical values of crude protein in several samples.     

PILOT PLANT EVALUATION OF INDIVIDUAL QUICK BLANCHING (IQB) FOR VEGETABLES

A pilot plant IQB blancher was field tested at a California freezing plant. The system included: a warming and drying preconditioning unit, a steam chamber for single layer belt heating, a deep moving-bed holding chamber for temperature equilibration and enzyme inactivation and an air-water spray cooling unit. IQB with and without preconditioning were compared to conventional, steam blanching at equivalent levels of enzyme inactivation in green beans, lima beans, Brussels sprouts and green peas. Effluent volume and total-solids concentration were measured. Product yields were determined by measuring residual peroxidase activity, chlorophyll conversion and ascorbic acid content as well as by sensory panel testing for color and flavor. Results showed that vegetables blanched with IQB and IQB with preconditioning were essentially the same in quality as those blanched at commercial conditions. Solids loss in the effluent was substantially less with IQB and preconditioning than with conventional steam blanching     

Effect of preliminary and culinary processing on amino acid content and protein quality in frozen French beans

The aim of the study was to evaluate the content of amino acids and protein quality of French bean pods. The investigated material consisted of the raw vegetable, fresh pods cooked to consumption consistency, and two kinds of frozen products stored for 12 months at ?20 °C and then prepared for consumption: frozen beans obtained using the traditional method (blanching before freezing) and frozen products of the ready‐to‐eat type (cooking before freezing). A comparison of the amino acid content in the product prepared for consumption showed that the lowest quantities were found in French beans obtained using the traditional method; products obtained using the modified technology and beans cooked directly after harvest had similar levels of most amino acids. The content of amino acids in 16 g N was less varied than in 100 g of the product. The protein in all the three products prepared for consumption as well as that in fresh bean pods hardly differs, as confirmed by the values in the essential amino acid index (EAA). The first limiting amino acid was methionine with cystine and the second was lysine.     

Essential Elements and Cadmium and Lead in Fresh, Canned, and Frozen Green Beans (Phaseolus vulgaris L.)

Sixteen essential elements, cadmium and lead were determined in fresh, canned, and frozen green beans (Phaseolus vulgaris L.). Samples were taken during processing to determine where changes in element content occurred. Canned green beans contained lower concentrations of calcium, copper, iron, magnesium, manganese, phosphorus, potassium, and zinc, but had higher amounts of chloride, nickel, and sodium than fresh beans. No change in silicon was observed. Iron, phosphorus and potassium were lower in frozen than in fresh green beans, but calcium, sodium and zinc were higher. There was no change in chloride, copper, magnesium, manganese and silicon due to freezing. Element retention ranged from 51 - 100% for canned and from 73 - 171% for frozen green beans.     

Protein content determination in Brassica oleracea species using FT‐NIR technique and PLS regression

Six fresh and one frozen vegetable cultivar groups possessing remarkably different morphology from the same Brassica oleracea species, including broccoli, Brussels sprouts, curly cabbage, white cabbage, red cabbage, cauliflower and white kohlrabi, were chosen to set up a Fourier transform near‐infrared spectroscopy (FT‐NIR)‐based method for the quantification of protein content. Sample preparation was based on lyophilisation and homogenisation. Calibration was set up with the help of the Kjeldahl method for the quantification of protein content in the range of 12.9–32.5 m/m%. Calibration model was developed using the spectral regions 1136–1334 and 1639–1836 nm, with partial least squares regression. This model was checked by cross‐validation. The performance of the final FT‐NIR estimation model was evaluated by root mean square of cross‐validation, root‐mean‐square error of estimation and the determination coefficient (R²). The final estimation function for the protein determination was characterised with the predictive error of 0.76 m/m% and R² value of 98.81.     

Effects of the methods of pre-treatment before freezing on the retention of chlorophylls in frozen leaf vegetables prepared for consumption

The investigation included kale, New Zealand spinach and spinach. The evaluation covered the raw material; the raw material after blanching; the raw material after cooking; and frozen products prepared for consumption after 0, 4, 8 and 12 months of refrigerated storage. Both the traditional method of freezing (blanching before freezing) and the modified method of freezing (cooked before freezing) were used in the experiment, as well as two storage temperatures, T = −20 °C and T = −30 °C. The content of chlorophylls in fresh kale was four times that in New Zealand spinach and 1.5 times that in spinach. With the exception of New Zealand spinach, blanching and cooking significantly reduced the content of chlorophylls. In kale products prepared for consumption, the content of chlorophylls decreased in each successive stage of the investigation. In products of New Zealand spinach and spinach, the losses were usually not significant. After 12 months of refrigerated storage, frozen kale products prepared for consumption retained 52–65% of total chlorophylls compared with the content in the raw material; products of New Zealand spinach and spinach retained 66–71%. In kale and New Zealand spinach, the content of chlorophyll a decreased more rapidly than that of chlorophyll b, while in spinach the converse was true. The kale products obtained using the modified method contained more chlorophylls, while in the two spinach species their content was lower. The lower storage temperature resulted in a higher retention of chlorophylls in vegetables.     

The amino acid composition of kale (Brassica oleracea L. var. acephala), fresh and after culinary and technological processing

The aim of the investigation was to evaluate the level of amino acids and the quality of protein in fresh and cooked leaves of kale and in two types of frozen product prepared for consumption after 12-months storage at −20 °C. Kale blanched before freezing (the traditional method) was cooked after refrigerated storage, while that cooked before freezing (the modified method) was defrosted and heated in a microwave oven. Both fresh and processed leaves of kale were a good source of amino acids. In all the samples, glutamic acid, proline and aspartic acid were the dominant, while lysine and leucine were the limiting amino acids. Cooked leaves contained 78% of the total amino acid content found in fresh leaves, while the traditional and modified frozen products contained 76% and 78%, respectively. The proportion of essential amino acids in total amino acids was 44% and 43%, respectively for fresh and cooked leaves and 46% for the frozen products. The lowest EAA index was found for the traditional frozen product (99); it was higher for the remaining samples, which were broadly similar to each other (105–106).     

Vegetables antioxidant losses during industrial processing and refrigerated storage

Twenty-five vegetables (artichoke, asparagus, beetroot, broad bean, broccoli, Brussels sprout, carrot, cauliflower, celery, chicory, cucumber, eggplant, endive, garlic, green bean, leek, lettuce, maize, onion, pea, pepper, radish, spinach, Swiss chard and zucchini) were used to evaluate their antioxidant activity. All fresh vegetables studied were able to scavenge lipoperoxyl and hydroxyl radicals. All the vegetables also presented good total capacity antioxidant by TEAC assay except cucumber, endive, carrot and zucchini.Vegetables stored (7 days) in a home refrigerator recorded the same antioxidant activity as fresh samples, except cucumber and zucchini (lipid peroxidation) and broccoli, Brussels sprout and leek (TEAC).Canned vegetables showed a more pronounced loss of antioxidant activity than frozen vegetables compared with fresh vegetables.During the shelf life of the processed vegetables (8 months for frozen and 18 months for canned vegetables), some products showed losses (19–48%) of their lipoperoxyl radical scavenging capacity and total antioxidant activity.     

Content of amino acids in raw and frozen broad beans (Vicia faba var. major) seeds at milk maturity stage,depending on the processing method

The aim of the present work was to evaluate the amino acid content in products obtained from broad bean seeds, at the milk maturity stage, and the quality of the protein in broad beans. The investigation included raw seeds, fresh seeds cooked to consumption consistency and two kinds of frozen products prepared for consumption: which were obtained using the traditional method (blanching the seeds before freezing) and the ready-to-eat type (cooking the seeds before freezing). Compared with the raw material, a similar (α = 0.01) content of amino acids in 100 g of the product was found in cooked fresh seeds. The seeds obtained from the ready-to-eat frozen product prepared for consumption contained higher amounts of all the amino acids than the traditional frozen product, and contained higher levels of some amino acids than were found in the product cooked from fresh seeds. Expressing the results per 16 g of N, the differences in the content of amino acids were much smaller. The limiting amino acid was cysteine with methionine (CS 74-86), the EAA index varying within the range 109–118.     

Assessment of cell damage in high-pressure-shift frozen broccoli: comparison with market samples

Pressure-shift freezing (PSF) is one of the most promising methods for obtaining high-quality frozen products. The aim of this work was to analyse the differences between broccoli that was frozen using two different PSF processes. In one of the processes, all the freezing was done inside the high-pressure vessel tempered at −20.5 °C. In the other process, the sample was taken out of the vessel after expansion, and freezing was completed using liquid N₂. Colour, texture, electrical conductivity, microstructure and drip losses after centrifugation were analysed and a sensory test was performed. The results were compared with those for conventionally frozen broccoli purchased at the market. PSF broccoli presented less cell damage, lower drip losses and better texture than the market samples. The two different PSF processes assayed produced no significant differences in the final quality of the samples.     

FLAVOR VOLATILES OF SOME COOKED VEGETABLES

SUMMARY– Using previously described sampling techniques, the flavor volatiles of a number of cooked vegetables were collected and analyzed by gas chromatography. The vegetables investigated were Brussels sprouts, cauliflower and runner beans and, in addition to the fresh vegetables, some preserved samples were examined. Quantitative measurements were made of the individual flavor components and the results were compared with those for fresh cabbage.     

Influence of blanching and low temperature preservation strategies on antioxidant activity and phytochemical content of carrots, green beans and broccoli

The objective of this study was to investigate the effect of blast freezing and blanching in combination followed by chilling, on the antioxidant activity (ARP), phenols, ascorbic acid and colour of broccoli, carrots and green beans. No significant changes (p > 0.05) in ARP of blanched frozen (BLFR) broccoli, carrot and green beans were observed. In contrast, UBFR (unblanched frozen) treatments caused a significant decrease (p < 0.05) in ARP and ascorbic acid content of vegetable samples. BLFR treated samples had better retention of antioxidant activity and ascorbic acid as compared to UBLR counterparts at chill storage (4 °C) for 7 days. However, no significant changes were observed in phenol content for all vegetables. Ascorbic acid decreased exponentially for both blanched and unblanched samples. The reaction rate constant (k) increased from 1.06 × 10⁻¹ day⁻¹ to 1.17 × 10⁻¹ day⁻¹ for blanched and unblanched broccoli florets and from 4.6 × 10⁻³ day⁻¹ to 1.98 × 10⁻¹ day⁻¹ for blanched and unblanched carrots during 7 days storage. Result presented here indicates greater stability of nutritional parameters for BLFR samples compared to UBFR samples during 7 days storage at 4 °C for all vegetables.