AU611155B2 - Post harvest treatment of produce - Google Patents

Description

r7 I -II-I 1 1 11111 6AOL~ 1 0 C, 0 u 0 el 00 0 0 010 0 0 0 0 0C 0 000 0 o 0 0 00 0 0 2. 3 0 00 0 110 2.0 0 330 0

L

ATTACH

MAKL OFFICC i

APPLICANT:

14UMI BVR: FILING DATE: WOBEL2A PTY. LIMITED PI 21941/87 2 M a y 3 3fl 0 0 1 03u li 00 0 o 0 FORM COMMONWEALTH OF AUSTRALIA The Patents Act 1952 COMPLETE SPECIFICATION FOR AN INVENTION ENTITLED: POST HARVEST TREATMENT c F The following statement is a full description of this invention, including the best method of performing it known -to me: -1- The Commissioner of Patents ij. 1 11 This invention relates to a post harvest treatment and, particularly, to post harvest treatment of fruit, vegetables, cut flowers and foliage.

Biocides have been used as a post harvest treatment on vegetable and fruit crops, cut flowers and foliage. These include root vegetables and leaf vegetables. Fruit crops are identified as pome fruit (apples and pears), stone fruit (cherries, plums, apricots, peaches and nectarines), citrus S0, 0(oranges, limes, lemons, mandarins and grapefruit), tropical (paw paws, 0o avodados, pineapples and mangos), berry (raspberry and loganberry, nuts S ooo 0 0 00 0o0 (walnuts, almonds and pistachios) and others.

000 0 ooo000000 S Fruit, vegetables, cut flowers and foliage are liable to attack from a wide variety of micro-organisms such as bacteria, yeast, mould arnd fungi. The 0 04 00 0 0 0 resulting attack manifests as rot, slime and growth on the exterior and 0 0 0 0 breakdown of the produce internally. It is to resist this attack that S 00 o o0 biocides are used.

Two classes of biocide have been used in these applications, inorganic °o 0 chlorine and complex organic biocides. Each of these has disadvantages.

S0 0 E The chlorine compounds such as sodium hypochlorite and calcium j hypochlorite are wide spectrum biocides, with a short residual life. Both these products are highly alkaline; such that, in continuous usage in a dip, the regular additions of hypochlorite raise the pH to a point where the chlorine can no longer dissociate into the biocidal HOCI species. In some rural areas the alkalinity and high pH of the supply water causes an immediate loss of biocidal activity by the same mechanism.

Testing the strength of the chlorine solution is complicated further by the fact that Ortho-Tolidine pH 2.0-2.5 and DPD diphenyldiamine, pH 6.3 both -2- Wobelea/62/May88 1, r> decrease the pH of the sample indicating effective free chlorine, whilst the actual dip at a pH of say 9.0 is actually ineffective.

Chlorinated cyanurates such as trichloro isocyanuric acid and sodium dichlor isocyanurate are more acidic in reaction. Although effective chlorination is in the right pH range 6.5-7.5. This low pH provokes another problem.

ooooo00000 0 0 o0 o Nitrogenous compounds, for example, amino acids, exuded from the cells of o 0 damaged produce react with chlorine to form chloramines. As the pH 000. drops below 7.5 the predominant chloramine is trichloramine.

oQoote O C Trichloramine, even at levels of 0.5 mg/l in the chlorine solution causes eye irritation of nearby workers.

o Of greater importance is the possibility of "chlorine" taint being picked up 0 0 o0 0 by the produce, for example, melons.

Irrespective of the chlorine type, a common problem with all these 0' compounds is corrosion. Iron dip tanks, brass gate valves and galvanised fittings suffer attack. As the resulting corrosion products, i.e. iron, copper and zinc, are kept within the system and accumulate with time, another factor comes into play.

Iron and copper together initiate a catalytic decomposition of the hypochlorite thereby reducing efficiency.

HOCI Catalyst O' HC1.

Organic biocides currently in use for post harvest use are, in general, of narrow spectrum and in consequence two or more may be combined to give the required cover of the organisms present -3- Wobelea/62/May88 0 0 4 o 0a oO o o oo0 00 0 00 o a 00 0 0 O 0 0 0 0 o u0 00 o o 00oo o o This lack of wide spectrum of control manifests itself in the following example.

Melons suffer attack from Rhizopus, Alternaria and Pseudomonas.

Organic biocide mixture A B gives control of these species but may not control, for example, a penicillium mould. The mould establishes itself during transit or storage resulting in down grading of the product.

The protectant dip becomes a source of infection which could be corrected by adding biocide C. Unfortunately product C is not compatible with product A.

The micro-organisms gradually acquire resistance so there is continuing pressure to get "new" biocides to overcome this problem.

In the field the biggest practical problem is keeping control of dip strenght, for example, not too low a concentration to get the required result. On the other hand, if the concentration is too high, burn damage or excessive residues may be found on the produce.

The majority of the organic biocides can only be assayed in a laboratory.

Due to the time taken to perform the assay, the result is, at best, of historical value.

Some of the biocides also suffer the disadvantage of incompatibility with chlorine, for example, they are difficult to use after a chlorine pretreatment unless a dechlorinator is used.

It is the object of the present invention to provide a post harvest treatment of fruit and vegetables which minimises these difficulties and which can -4- Wobelea/62/May88 1 readily be controlled on site.

The invention, in its broadest sense, a post harvest treatment of fruit, vegetables, cut flowers or foliage comprising washing the product with a biocide comprising an aqueous solution of an chloro, bromo, or chlorobromo organic complex which disassociates to provide free halogen and controlling the pH of tie solution to maintain the required degree of dissolution of the biocide.

Preferably the biocide may be an imidazole or a hydantoin.

One specific suitable biocide is I-bromo-3-chloro-5,5-dimethyl-hydantoin 0oo

(BCDMH).

o o| The biocide could be selected from the group consisting of 0 00 0o o trichloroisocvanurlc acid (TRICHLOR, TICA); sodium dichloroisocyanurate S0 o0 (DICHLOR) and bromochlorotetramethylimidazolinone.

Preferably, the biocide can be used either as a spray or a clip and, if used as a spray may be used either as a recirculating spray or a non-recirculating spray.

4 0 If the BCDMH is used as a recirculated spray or a dip, we prefer to use a concentration of 25-50 mg per litre of BCDMH at pH 9.5 or, if as a nonooo recirculated spray, at a concentration of 5-10 mg per litre at a pH of 7 to The effective active concentration for each of these is 5-10 mg per litre.

L The compound has not been used as a biocide in the treatment of fruit and Uw vegetables.

S U Wobelea/62/Mar9l

P

It is preferred that, after the fruit or vegetables have passed through the primary treatment process, then a secondary, long term, protectant cen be t I I t 0 a 1 0 a e 0o Iio o Wobelea/62/Mar91 1_ applied, which protectant can include sodium metabisulphate and copper sulphate to provide SO 2 and Cu ions.

In each case, the concentration of the active components can readily be checked in the field.

In order that the invention may he more readily understood, we shall describe certain different embodiments of the invention.

In the first of these, we use a non-recirculated spray and, for this, we use 0 o -o BCDMH in a concentration of 5-10 mg per litre of water at a pH of 7 to 0 °0000 oooo O C To maintain the concentration required the BCDMH is metered by Redox a a control, and, as there is n- recirculation, then the optimum concentration can be achieved.

0 1 As discussed hereinafter, the concentration can readily be tested on site.

In a second arrangement, where we use either a dipping tank or a recirculating spray, we prefer to use n composite of active ingredients which comprises:- BCDMH 5%6 STP 16% Sodium Metasilicate 8% Surfactant 3% Silica 2% Sodium Sulphate 66% -6- Wobelea/62/May88 ,I We prefer to use this mixture at a concentration of 25-50 mg per litre BCDMH at a pH of 9.5 and the current effectiveness of this product can be checked in the field by using proprietary test strips for bromine/chlorine alkalinity and pH. The resulting pH and alkalinity result in a solution which balances on the Langlier scale to prevent corrosion of pumps, filters and pipework Again, in the operation of the process a Redox controller is used to monitor and to dose the product.

The biocide of the invention has been found to he effective in a relatively short time.

°o For example, for pseudomonas aeruginosa at 90-1500 c.f.u. ml, if the product is used at the 5 mg per litre concentration mentioned previously, then there is a 99.99% kill in twenty seconds.

If the concentration drops to, say, 3 mg per litre, there is still a 99.99% kill o° in sixty seconds.

Thus, a particular operator would have to decide where, 'ithin these ranges, he wished to use the product.

t As mentioned earlier, we propose using at the higher end of the concentration, which is still well below a level which would leave a toxic quantity of compound on the fruit or vegetables, to obtain the relatively short necessary contact time.

If waxy products or products which are otherwise hard to wet are to be tested, then it may be necessary to add to the solution an acceptable surfactant, and this is included in the formulation given.

-7- Wobelea/62/May88

L.

~111~ C_ C~_ 0 O0 0 0 000 C 00 0 0 o 000 00o o o o Basically, the fruit or vegetable products which has passed through the process of the invention are biologically clean as the process will have an equivalent kill as that described above in respect of yeasts, moulds, fungi, algae and bacteria.

The invention may provide a secondary process, which not only provides long term protection for the product, but also acts to destroy any organo halogen which is carried over on the product.

We have previously indicated that, at the concentrations at which crgano halogen is used, there can effectively be insufficient carry over to provide any health risk but this secondary treatment removes even such risk.

The secondary treatment uses sulphur dioxide in concentration between 200 and 400 mg per litre and Cu ions in concentration between 10 and 100 m, per litre.

A preferred composition may be- 'Vater NaOH Sodium Metabisulphite Citric Acid CuSO4 .5H 2 0 Surfactant Water to 1000 litres 750 litres 15 kg 62.5 to 250 kg 100 kg 12.5 to 50 kg 10-20 kg This can be diluted 1:100 to 1:400 depending on the activity required.

For example, if 250 kg of sodium metabisulphite and 12.5 kg of CuSOt, are Wobelea/62/May88

I

U used and the solution, in turn, is diluted 1:400, then the active ingredients are:- S02 400 mg per litre Cu+"Cu 1 10 mg per litre.

For cut flowers and foliage, sugars, such as dextrose, sucrose, fructose and glucose are incorporation in the composition to provide a food source.

The effectiveness of the solution is again a concentration against time Sfunction, i.e. a 'pulse dip' of 5 30 mins using an increased concentration may be similar in effect to continuous standing in a solution having a lower concentration.

For longstanding solutions, additional protection for cut flowers is obtained by incorporating ethylene blockers or absorbers such as AOAA and other metal complexes.

It is the sulphur dioxide which effectively destroys any halogen which is carried over the these two provide long term protection.

After some time the Cu+ ions will be air oxidised to Cu++ ions which are considered non-toxic and the sulphur dioxide will have a life which is less than the copper, thus leaving the product fully safe to use.

Further, by the use of a strong oxidizer followed by a strong reducing agent, the biocide effect is maximised over the total spectrum of algae, bacteria, yeast, mould and fungi.

Whilst we have suggested a specific concentration of this product, if a -9- Wobelea/62/May88 m II I shorter contact time is to be used, then this concentration can be increased whilst still providing a protected product which has a level of toxicity which is within the accepted range.

For this product, testing can be effected by commercial test strips for 300 mg per litre of copper and further commercial test strips are available for concentrations of between 10 and 500 mg -pr litre of sulphur dioxide.

Thus, in this aspect, once again, there is a cheap and simple way of checking the concentrations which has not previously been able to be done.

It will be appreciated that the use of the particular product of the invention provides improved control of the concentration of the active ingredients as checking this is very much simpler than has previously been the case, and can be done automatically with a redox probe controlled 0 .dosing system.

0 oo The process can also limit corrosion of the equipment used in the C: treatment, which limitation also ensures that the loss of activity due to the existance of metal ions is controlled.

Further, both parts of the process give a wide spectrum control.

Provided the pH is maintained below 9.5, the performance of the system is unaffected by the presence of electrolytes.

For example, NaCI, CaCI 2 CaS04 and NaHCO 3 can be used to increase the specific gravity of the solution to float produce, such as pears.

Whilst we have described herein particular compositions of the treatment products to be used and preferred concentrations and times, it will be Wobelea/62/May88 appreciated that it is open to particular operators to vary these parameters to optimise the treatment process whilst, at the same time, ensuring that the treated product is completely safe for use.

-11- Wobelea/62/May88 r

Claims (13)

1. A post harvest treatment of fruit, vegetables, cut flowers or foliage comprising washing the product with a biocide comprising an aqueous solution of an chloro, bromo, or chloro-bromo organic complex which disassociates to provide free halogen and controlling the pH of the solution to maintain the required degree of dissolution of the biocide.

2. A treatment as claimed in claim I wherein the biocide is an imidazole or a hydantoin.

3. A treatment as claimed in claim 2 wherein the hiocide is a hydantoin and is I-bromo-3-chloro-5,5-dimethyl-hydantoin (BCDMH).

4. A treatment as claimed in claim 1 wherein the biocide is selected from the group consisting of trichloroisocvanuric acid (TRICHLOR, TICA); sodium dichloroisocyanurate (DICHLOR) and bromocl-horotetramethylimidazolinone. The treatment of claim 1 or claim 2 wherein the aqueous solution is used as a recirculating or non-recirculating spray or as a dip.

6. A treatment as claimed claim 5 wherein, when the biocide is BCDMH and it is used as a recirculating spray or dip, the concentration is mg per litre at pH 9.5 and, when as a non-circulating spray, the concentration is 5-10 mg per litre and the pH 7 to Wob /iM Wobelea/62/Mar91 II I ll _lI 1 I i] Known to me: S-1-

7. A treatment as claimed in any one of claims 1 to 6 where the required concentration of the biocide is achieved by a probe controller which effects the operation of a feeder.

8. A treatment as claimed in any preceding claim wherein, after the primary treatment process, a secondary treatment process is used and in this process sulphur dioxide and Cu+ ions are brought into contact with the product.

9. A treatment as claimed in claim 8 wherein the sulphur dioxide is obtained from sodium metabisulphite and the Cu+ ions from copper sulphate. A treatment as claimed in any one of claims I to 3 wherein the biocide for the treatment is a mixture which includes BCDMH, STP, sodium metasilicate, surfactant, silica and sodium sulphate.

11. A treatment as claimed in claim 10 wherein the BCDMHI comprises by weight of the compounds.

12. A treatment as claimed in either claim 10 or claim 11 wherein the mixed compounds are dissolved in water at a concentration of 25-50 mg per litre and the pH is

13. A treatment as claimed in any preceding claim wherein the solution contains an electrolyte to increase the specific gravity thereof. Wobe lea/62/Mar91 Wobelea/62/Mar91 F_ fact that Ortho-Tolidine pH 2.0-2.5 and DPD diphenyldiamine, pH 6.3 both -2- Wobelea/62/May88 mum i lii ii i

14. A treatment as claimed in claim 13 wherein the pH of the electrolyte is less than A treatment as claimed in claim 13 or claim 14 wherein the electrolyte is selected from the group containing NaCI; CaCI 2 CaSO4 and NaHCO 3

16. It is a treatment as claimed in claim I and substantially as hereinbefore described with reference to the examples. o 0 o DO 0 000 0 00 0 O11 S 1 I Dated this 14th day of March, 1991 WOBELEA PTY. LIMITED By Its Patent Attorneys A. Tatlock Associates 1 Wobelea/62/Mar9l -1-