BLEACHING AND STERILIZATION OF CORK ARTICLES

Abstract: Cork articles are bleached and/or sterilized by first contacting with a hydrogen peroxide solution, followed by contacting with a solution of the enzyme catalase. The quality of the treated cork articles can meet the usual industry requirements in terms of residual H2O2, mechanical properties, etc. H2O2 can be removed down to very low levels, even when high concentrations of peroxide are used. Rinsing after the treatment with peroxide is generally unnecessary. The catalase solution can be used repeatedly. The total processing time can be kept short, e.g. about one hour in total for the peroxide treatment and the catalase treatment. The BOD and COD of the waste water are low, and the quantity of waste water can be reduced by repeated use of the same catalase bath.

Description: BLEACHING AND STERILIZATION OF CORK ARTICLES TECHNICAL FIELD This invention relates to a method for bleaching and/or sterilizing cork articles, such as cork stoppers BACKGROUND ART Cork stoppers for use in wine bottles etc. have commonly been bleached and sterilized by a treatment with hypochlorite at alkaline pH, followed by a treatment with oxalic acid. However, the use of hypochlorite increases the risk of forming undesirable chlorinated organic compounds and provides inadequate protection o f the cork against subsequent microbial contamination and growth. Bleaching of cork stoppers with hydrogen peroxide (H 2 0 2 ) has therefore become increasingly common. A residual content of H 2 0 2 is generally unacceptable in cork stoppers to be used in food and beverage products. Thus, residual H 2 0 2 can be detrimental to bottled wine, reducing sulfur dioxide content and causing oxidation. Commonly, the cork articles are treated by immersion in a peroxide bath, followed by rinsing, immersion in a citric acid bath, drying and resting. Depending on the peroxide concentration, the resting time can be up to several weeks. This process has the disadvantage of a very long total processing time, and further the removal is not efficient when high concentrations of hydrogen peroxide are used. Furthermore, disposal of the spent citric acid bath involves a large quantity of waste water with high values of BOD and COD. A variety of other processes have therefore been proposed within the last 10 years for bleaching of cork stoppers with H 2 0 2 and removal of residual H2O2 from the cork stoppers after the bleaching. Thus, US 4,693,757 proposes washing with alkali, followed by a short-time treatment with hydrogen peroxide and hot-air drying. FR 2,569,369 and FR 2,635,292 propose processes which include washing with an alkaline solution of H 2 0 2 , followed by washing with an acidic solution and drying. FR 2,639,282 proposes a process which includes sprinkling the cork stoppers with an alkaline solution of H 2 0 2 in a rotating drum, followed by blowing hot air and expelling the evolved gases. US 5,098,447 proposes impregnation with H 2 0 2 and alkali, followed by drying by exposure to ultraviolet radiation. F. Puerto, .Revue des Oenologues , 18 (64) , 21-26 (1992) and F. Puerto, "Sevi " Num. , 2.541, 1.195-1.198 (1993) describe a process for "controlled peroxide washing" comprising spraying the cork stoppers with a liquid at neutral pH and low content of H 2 0 2 , followed by drying at controlled temperature . It is the object of this invention to provide an improved process for bleaching and/or sterilizing cork articles with H2O2 and removing residual H 2 0 2 from the cork articles. STATEMENT OF THE INVENTION We have developed an improved process wherein the cork articles are first contacted with a hydrogen peroxide solution, followed by contacting with a solution of the enzyme catalase. The quality of cork articles treated by this process can meet the usual industry requirements in terms of residual H 2 0 2 , mechanical properties etc. We have found that with this process it is possible to remove H 2 0 2 down to very low levels, even when high concentrations of peroxide are used. Further, the rinsing step after the treatment with peroxide can be omitted, leading to a simplified process with two baths instead of three in the conventional citric acid process. The process of the invention is economical because the catalase solution can be used repeatedly, so only a small amount of catalase is used instead of a much larger amount of citric acid in the conventional process. We have also found that the total processing time can be kept short, e.g. about one hour in total for the peroxide treatment and the catalase treatment. In addition, the waste water problems can be reduced because the BOD and COD of the waste water are low, and because the quantity of waste water can be reduced by repeated use of the same catalase bath. DETAILED DESCRIPTION OF THE INVENTION Cork articles The process of the invention is applicable to any cork article requiring bleaching and/or sterilization, such as tiles, sheets and stoppers. In particular it may be applied to cork articles for use in the food or beverage industry, e.g. cork stoppers for wine bottles. Treatment with hydrogen peroxide The contact with hydrogen peroxide serves to effect the desired bleaching and/or sterilization of the cork articles. The H 2 0 2 concentration in the bath may be chosen as required to achieve the required degree of bleaching and sterilization, typically in the range 10-500 g/l. A high concentration, e.g. 100-500 g/l may be preferred to achieve a very efficient bleaching and sterilization, and advantageously the process of the invention allows efficient H 2 0 2 removal, even at such high concentrations. The hydrogen peroxide bleaching can be performed in a conventional manner. Typical conditions include a contact time in the range of 10-60 minutes (particularly 15-30 minutes) at an alkaline pH (e.g. pH 10-11) and a temperature near ambient, e.g. 20-70°C. Optionally, other additives known in the art may be included in the H 2 0 2 solution, such as stabilizers for H 2 0 2 and surfactants. The H 2 0 2 solution may further comprise NaOH and/or peracetic acid for improved effect. The cork articles may be brought into contact with the solution of H 2 0 2 by any convenient method, e.g. by immersing the cork articles in the solution or by spraying the solution onto the cork articles. The contact with H 2 0 2 can be followed by a rinsing with water, before the contact with catalase, but this rinsing step is usually not needed, and it is preferred to avoid it, resulting in a simpler process. Catalase The catalase to be used is an enzyme that catalyzes the disintegration of hydrogen peroxide. It has the Enzyme Nomenclature number EC 1.11.1.6. It is preferred to use a catalase which has good activity and stability at the process conditions which may include alkaline pH and high H 2 0 2 concentration. It is preferred to use a catalase derived from a microorganism since such enzymes can be produced economically. The catalase is preferably derived from a strain of the genus Aspergillus, Scytalidium, Humicola , Penicillium Thermoascus, Acremonium, Zoogloea , Thermus , Micrococcus or Hansenula, particularly the species A . niger, A . terreus, S. thermophilum, H. insolens, M. luteus or M. lyzodeicticus. The catalase may be produced according to WO 92/17571 (Novo Nordisk A/S) , JP-A 2- 76579 (Novo Nordisk A/S) , JP-A 63-3788 (Mitsubishi Gas Chemical) , JP-A 4-20288 (Kurita Water Industries) , WO 93/18166 (Genencor Int'l) , JP-A 7-163342 (Mitsubishi Gas Chemical) , JP-A 5-153975 (Mitsubishi Gas Chemical) , JP-A 62-228271 (Nippon Peroxide) or JP-A 55-135588 (Mitsubishi Petrochemical) . Some commercially available catalase preparations for use in this invention are Catazyme * , Novozym * 355, Terminox * 10L and Terminox Ultra 50 (products of Novo Nordisk A/S) ; Kuribata™ K-310, X -502 Reyonet™ (product of Nagase) , Oxydex™ and Ask Super™ 25 (Mitsubishi Gas Chemical) . Contact with catalase The contact with catalase serves to remove H 2 0 2 from the cork articles to a degree which is acceptable for the intended use of the articles. Typically, more than 90% (e.g. more than 95%, and even more than 99%) of the H 2 0 2 will be removed. In a preferred embodiment, the same catalase bath is used repeatedly two or more times, e.g. 2-20 times, particularly 5-10 times, to reduce the costs for catalase and for waste water treatment . A convenient schedule may involve using the same catalase bath repeatedly throughout one working day (e.g. 5-10 times) and then disposing of the spent bath at the end of the day. Advantageously, the catalase bath was found to retain its efficiency throughout this schedule. The contact with catalase can be done e.g. by immersion of the cork articles in a catalase bath or by spraying with a catalase solution. In a preferred embodiment, the contacting comprises immersing the cork articles in a catalase bath, removing them from the bath and holding them outside the bath for a resting period. Advantageously, it has been found that the catalase continues to act throughout the total contact time of immersion and resting. It is usually convenient to use a total contact time of 10-60 minutes, particularly 20-40 minutes. For a contact time in this range, a suitable enzyme dosage will generally be in the range 1-1000 kCIU/1, particularly 10-100 kCIU/1 (1 kCIU = 1000 CIU, catalase activity unit defined below) or 0.01-1 mg/1 of pure enzyme protein. A suitable temperature for the treatment is in the range 5-70°C, preferably 20-60°C. Generally, no pH adjustment is needed. After the catalase treatment, the cork articles can optionally be rinsed with water and/or dried by conventional methods. Methodo1ogies The following methodologies are referred to in this specification: Catalase activity determination One CIU is defined as the amount of enzyme that decomposes 1 μmole of H 2 0 2 per minute at pH 7.0, 25°C, while the H 2 0 2 concentration decreases from 10.3 to 9.2 μmoles per ml in the reaction mixture. Determination of resistance to compression This is determined following the ISO 9727. Determination of dimensional recovery This is obtained as a % of diameter recovery, 15 minutes after compression to 33% of cork stopper diameter at 1 cm/min compression rate. Solid residues This is determined by immersing the cork stoppers in 10% alcohol adjusted to pH 3.5 with tartaric acid, shaking for 20 minutes, filtering the alcoholic extract through 0.45 μm porosity filters. Sensory analysis 30 cork stoppers are immersed in about 10 ml of "standard wine" (Portuguese "verde" white dry) so as to allow 5 mm of the cork stopper to be in contact with the wine. After standing in this way for 24 hours, sensory analysis is performed classifying olfactive characteristics of wine according to the following scale: 0 - Bad, 1 - Mediocre, 2 - Tolerable, 3 - Sufficient, 4 - Good, 5 - Very good Generally, a panel of 30 is used, and a weighted average of the individual results is calculated. Visual quality This test is performed by visually comparing the appearance of cork stoppers treated according to the invention with cork stoppers treated by a conventional method (with citric acid) . EXAMPLES Example 1 Treatment of cork stoppers at various contact times and enzyme concentrations In each of the following experiments, 100 cork stoppers were treated as follows: - 5 minutes immersion in a peroxide bath, volume 10 liter, H 2 0 2 concentration 69-86 g/l, - 30 minutes resting after removal from the peroxide bath, - immersion in a catalase bath, volume 10 liter, concentration and contact time as shown below, - resting after removal from the catalase bath, resting time shown below. Two types of catalase were tested: Terminox (from Scytalidiiuπ) and Catazyme (from Aspergillus niger) . The residual quantity of peroxide was measured after the treatment. The results were as follows : Enzyme Immersion Resting time Peroxide concentra¬ time in enzyme after enzyme quantity tion bath bath (mg/cork (kCIU/1) (minutes) (minutes) stopper) Terminox Catazyme 25 0 0 16.7 16.7 25 10 0 0.83 0.58 25 10 10 0.83 0.17 25 10 20 0.33 0.07 25 10 30 0.33 0.07 25 10 40 0.17 0.07 25 10 50 0.17 0.02 50 0 0 16.7 16.7 50 10 0 0.83 0.17 50 10 10 0.33 0.07 50 10 20 0.33 0.07 50 10 30 0.17 0.04 50 10 40 0.07 0.01 50 10 50 0.07 0.00 100 0 0 16.7 16.7 100 10 0 0.83 0.07 100 10 10 0.17 0.02 100 10 20 0.17 0.02 100 10 30 0.07 0.01 100 10 40 0.07 0.00 100 10 50 0.07 0.00 These results show that both types of catalase are effective for the removal of peroxide from the cork stoppers. The catalase from A. niger was found to be particularly effective. It is seen that a longer resting time improves the peroxide removal, i.e. the catalase continues to act throughout the total contact period of immersion and resting. It is seen that even at the lowest enzyme concentration tested (25 kCIU/1) , 99% removal of peroxide was achieved in 20 minutes total contact enzyme (immersion + resting) for the A . niger enzyme, and in 50 minutes total contact time for the Scytalidium enzyme. At a higher dosage of the A . niger enzyme, hydrogen peroxide could be removed to below the detection limit (99.9 % removal) . Example 2 Effect of peroxide concentration and catalase contact time Cork stoppers were treated in the same manner as in Example 1, except that the catalase concentration was kept at 100 kCIU/1, and the peroxide concentration and catalase contact time were varied as shown below. The results were as follows: Peroxide Immersion Resting time Peroxide concentrat time in after enzyme quantity ion (g/l) enzyme bath bath (mg/cork (minutes) (minutes) stopper) Terminox Catazyme 40-45 0 0 6.67 6.67 40-45 10 0 0.07 0.07 40-45 10 10 0.02 0.02 40-45 10 20 0.02 0.00 40-45 10 30 0.02 0.00 40-45 10 40 0.02 0.00 40-45 10 50 0.00 0.00 70-75 0 0 16.7 16.7 70-75 10 0 0.83 0.07 70-75 10 10 0.17 0.02 70-75 10 20 0.17 0.02 70-75 10 30 0.07 0.00 70-75 10 40 0.07 0.00 70-75 10 50 0.07 0.00 100-110 0 0 16.7 16.7 100-110 10 0 0.83 0.17 100-110 10 10 0.83 0.17 100-110 10 20 0.33 0.07 100-110 10 30 0.17 0.07 100-110 10 40 0.17 0.02 100-110 10 50 0.07 0.00 175-180 0 0 16.7 16.7 175-180 10 0 0.83 0.17 175-180 10 10 0.83 0.07 175-180 10 20 0.33 0.07 175-180 10 30 0.33 0.02 175-180 10 40 0.17 0.02 175-180 10 50 0.17 0.00 These results show that the peroxide can be removed effectively from the cork stoppers at all peroxide concentrations in the range of 40-180 g/l. Example 3 Repeated use of catalase bath In this example, a total of 10 washings were performed using the same enzyme bath repeatedly. The procedure of the previous examples was used at the following conditions: - peroxide concentration 220 g/l, - contact time of cork stoppers with peroxide bath: 15 minutes, - enzyme used: Catazyme - enzyme concentration: 15 kCIU/1 - contact time with enzyme bath: 10 minutes - resting time after the enzyme bath: 20 minutes. The results after each repetition were as follows: Washing Immersion Resting time Peroxide number time in enzyme after enzyme quantity bath bath (mg/cork (minutes) (minutes) stopper) 0 0 0 30.0 1 10 20 0.17 2 10 20 0.17 3 10 20 0.17 4 10 20 0.33 5 10 20 0.17 6 10 20 0.17 7 10 20 0.33 8 10 20 0.33 9 10 20 0.17 10 10 20 0.17 These results show that 99 % removal or better can be achieved with an enzyme concentration of 15 kCIU/1 using 10 minutes contact time + 20 minutes resting time. The results also show that the catalase bath can be used repeatedly up to 10 times without any deterioration of performance. Example 4 Treatment at industrial scale Cork stoppers were treated at industrial scale by immersion in peroxide bath, rinsing, immersion in enzyme bath, rinsing, and drying. The enzyme used was Catazyme, and the process conditions were as follows: - Number of cork stoppers: 50,000 - volume of peroxide bath: 400 1 - concentration of peroxide bath: 130 g/l - contact time of cork stoppers with peroxide bath: 20 minutes - volume of enzyme bath: 400 1 - concentration of enzyme bath: 25 kCIU/1 - contact time of cork stoppers with enzyme bath: 10 minutes Peroxide quantity change along the washing process was measured, and the results were as follows: Washing stage Peroxide quantity (mg/cork stopper) After immersion In 16.7 peroxide bath After rinsing 1.67 After immersion in enzyme 0.17 bath After rinsing 0.17 After drying 0.00 The above results show that peroxide can be removed to below the detection limit (99.9% removal) by the process described above. Next, the cork stoppers were evaluated after drying by the following methods. Commonly accepted industry standard values are shown for comparison. Property Measured Recommended Resistance to compression Fl=70 Fl=65 ± 15 (daN) F2=40 F2 > 20 Dimensional recovery (%) 99 > 96 Solid residues (mg/cork 1.7 < 2.5 stopper) Sensory analysis (average 3.3 classification) The quality of the cork stoppers meets accepted industry standards with a sensory classification of "sufficient" to "good" . Example 5 Treatment at industrial scale with high peroxide concentration Cork stoppers were treated at industrial scale by immersion in peroxide bath, resting, immersion in enzyme bath, resting, and drying. The enzyme used was Catazyme, and the process conditions were as follows: - Number of cork stoppers: 100,000 - volume of peroxide bath: 200 1 - concentration of peroxide bath: 370 g/l - contact time of cork stoppers with peroxide bath: 30 minutes - resting time after peroxide bath: 12 hours - volume of enzyme bath: 200 1 - concentration of enzyme bath: 20 kCIU/1 - contact time of cork stoppers with enzyme bath: 15 minutes The following results were obtained by testing the cork stoppers after drying: Resistance to compression (daN) Fl=66 F2=36 Peroxide quantity (mg/cork 0.0 stopper) Dimensional recovery (%) 97 Solid residues (mg/cork stopper) 0.8 Sensory analysis (average 2.9 classification) The above results demonstrate that a satisfactory quality of cork stoppers was also obtained at these conditions. Example 6 Repeated use of Catazyme bath A total of 5 consecutive washings were performed using the same enzyme bath repeatedly. The following conditions were used for each treatment: - Number of cork stoppers: 50,000 - volume of peroxide bath: 400 1 - concentration of peroxide bath: 130 g/l - contact time of cork stoppers with peroxide bath: 15 minutes - resting time after peroxide bath: from 0 to 17 hours - volume of enzyme bath: 400 1 - concentration of enzyme bath: 15 kCIU/1 - contact time of cork stoppers with enzyme bath: 10 minutes -resting time after the enzyme bath: 20 minutes The quantity of peroxide was measured along the washing process. Results: Washing 1 2 3 4 5 After immersion in peroxide 16.7 8.30 1.67 16.7 1.67 bath After rinsing 1.67 0.83 0.17 3.33 0.17 After immersion in enzyme 0.07 0.17 0.07 0.17 0.07 bath After 10 minutes of resting 0.07 0.07 0.02 0.07 0.02 After 20 minutes of resting 0.02 0.02 0.00 0.02 0.00 After 30 minutes of resting 0.02 0.02 0.00 0.02 0.00 After drying 0.00 0.00 0.00 0.00 0.00 Also, the quality of the treated cork stoppers was measured at the end of each treatment. Results: Washing Resistance Dimension Solid Sensory to al residues analysis compressio recovery (mg/cork n (%) stopper) (average (daN) classificatio n) 1 Fl=65 97 0.2 2.7 F2=40 2 Fl=74 98 0.2 2.3 F2=45 3 Fl=70 97 0.2 2.8 F2=40 4 Fl=68 96 0.4 2.8 F2=38 5 Fl=66 98 0.3 2.4 F2=38 It is seen that with an enzyme concentration of 130 g/l and a total contact time of 30 minutes (10 minutes immersion + 20 minutes resting) , the hydrogen peroxide could be completely removed. The properties of the cork stoppers after the treatment met industry standards. No change of the enzyme performance could be seen after repeated use. Example 7 Determination of BOD and COD Samples of the peroxide bath and the enzyme bath were collected at the end of the experiment described in the previous example, and the COD and BOD were determined. Further, equal parts of peroxide bath and enzyme bath were mixed and incubated for 12 hours before determining COD and BOD. For comparison, COD and BOD were also determined for a used citric acid bath from a conventional process. Test COD (mg 0 2 /l) BOD (mg 0 2 /l) Peroxide bath 15 690 not determined Enzyme bath 1 070 240 (Peroxide + enzyme) 1 630 46 bath Citric acid bath 1 650 656 Admissible values 150 40 The above results show that the COD and BOD of the enzyme bath were lower than for the citric acid bath, while the quantity was reduced due to the repeated use of the enzyme bath. It is seen that mixing the peroxide bath and the enzyme bath and holding the mixture gives a further significant reduction of the BOD and COD values.

Claims: CLAIMS 1. A method for bleaching and/or sterilizing cork articles, comprising a) contacting the cork articles with an aqueous solution of hydrogen peroxide and subsequently, b) contacting the cork articles with an aqueous solution of a catalase. 2. The method of the preceding claim wherein the hydrogen peroxide in step a) is present at a concentration of 10-500 g/l, preferably 100-500 g/l. 3. The method of either preceding claim wherein the contacting in step a) is continued for 10-60 minutes. 4. The method of either preceding claim, which does not comprise a rinsing step between steps a) and b) . 5. The method of any preceding claim wherein the contacting in step b) comprises immersing the cork articles in a bath of the catalase solution, followed by removing the articles from the solution and holding the articles outside of the bath. 6. The method of any preceding claim wherein the contacting in step b) comprises immersion in the catalase solution, and wherein the catalase solution is used 2-20 times. 7. The method of any preceding claim wherein the contact with catalase in step b) is continued for 10-120 minutes. 8. The method of any preceding claim wherein the catalase is present in step b) at an activity of 1-1000 kCIU/1. 9. The method of any preceding claim wherein the catalase is derived from a strain of Aspergillus or Scytalidium. 10. The method of any preceding claim, further comprising rinsing with water after step b) . 11. The method of any preceding claim, further comprising a final drying step.

Inventors: CONRAD LARS SPARRE, GOMES MARIA DA CONCEICAO, MARTINEZ RAMIRO, NETO PAULA VIEIRA, CONRAD, LARS, SPARRE, GOMES, MARIA DA CONCEICAO, MARTINEZ, RAMIRO, NETO, PAULA, VIEIRA
Applicants: CONRAD LARS SPARRE, GOMES MARIA DA CONCEICAO, MARTINEZ RAMIRO, NETO PAULA VIEIRA, NOVONORDISK AS, CONRAD, LARS, SPARRE, GOMES, MARIA DA CONCEICAO, MARTINEZ, RAMIRO, NETO, PAULA, VIEIRA, NOVO NORDISK A/S
Application year: 1996
Main classification: B27K7
IPC codes: B27K7