NZ240112A - A process for removing calcium oxalate from plant tissue - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £4011 £ % A 1 Priority i?o £>; ip. f(Q Complete Si.o.: 'r:.. . .V.'.Q; Class: £-> ,^v-:....

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^ P ,T « >1 -«B MJ ' • a ■Jaj-' v M Patents Form No. 5 Number > "4 OCT 199]'' *, ;PATENTS ACT 1953 Dated ^ - ;COMPLETE SPECIFICATION ;I ;REMOVAL OF CALCIUM OXALATE ;We, COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ;LO^-OIVX £><^£-ANvrPyr iohj ;CORPORATION-, a company organised under the laws of the State of the Australian Capital Territory, of Limestone Avenue, Campbell, Australian Capital Territory 2601, Australia do hereby declare the invention for which I/we pray that a Patent may be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement: ;- 1 - (Followed by page la) ;The present invention relates to a process for the removal of calcium oxalate crystals from plant tissue, 5 particularly tissue which is processed to make food. In add it ion the present invention relates to a product produced by this process. ;Backg round of Invent ion ;Consumers of kiwifruit and other foodstuffs 10 (Monstereo Delicioso, banana peels, taro) may suffer from an unpleasant sensation sometimes referred to as "catch-in-throat" caused by the presence of needle-like crystals of calcium oxalate called raphides. Consumption of fresh kiwifruit rarely if ever results in a 15 " catch - in - throat" because the needle shaped raphides are contained in large sacs called idioblasts. (See, ;Kiwifruit: Science and Management, P. 61, 64 & 83 "In kiwifruit the raphides are particularly large - enormous, ;long crystals in idioblasts or sacs, apparently surrounded 20 by mucilage." "Large raphide cells are found in the palisade and spongy mesophyll, alongside the veins, in the teeth along the margin of the leaf and in the hairs." ;"Raphide cells were found (van Tieghem 1899) in all tissues but particularly in the ovary, where individual 25 raphide cells reached 600-800um in length and 70-90um wide). ;Ingestion of oxalate by humans is associated with renal damage such as nephrolithiasis due to the deposition of oxalate crystals in the kidney and bladder. 30 The present inventors have found that substantial concentrations of calcium oxalate as needle-like crystals (raphides) occur in kiwifruit. When the crystals are separated, washed and consumed they impart a "catch-in - throat" unpleasant sensation. These crystals ( ;c \ ;35 may be observed under a low power microscope. X-Ray ;' 4 0C7* F99 f i: V diffraction of the crystals confirmed that they were calcium oxalate.

The crystals in kiwifruit, for example, are released from their sacs when the fruit is damaged. When pulp is 5 manufactured crystals are found in the finished product which, when consumed imparts the unpleasant sensation to the consumer referred to as "catch-in-throat".

A similar acridity is found when the giant taro and other aroids are consumed. Boiling the aroids for long 10 periods has been found to reduce the acridity, however, this technique is not suitable for kiwifruit as the product would lose its organoleptic properties.

Summary of the Invention The present inventors have observed that when pulped 15 kiwifruit is passed through a centrifuge the (raphides) needle-like crystals are concentrated in the retained solid stream while the liquid stream is essentially free of the crystals. Separation occurs because the specific density of the crystals (2.2g/cm3) is greater than that 20 of the other food components. Once separated the product can be safely consumed and no "catch-in-throat" is noticed.

This invention may also be used to remove oxalate from foods by adding a sufficient amount of a soluble calcium salt to precipitate oxalate as calcium oxalate. 25 This approach is used (see for example FRANCO and KRINITZ, 1973 "Determination of Oxalic Acid in Foods" JAOACS 56, No. 1, P.164--166) for the analysis of oxalates in foods but has not been applied for the improvement of foods containing oxalates.

Such a process could make oxalis suitable as fodder or reduce the oxalate content of vegetables such as rhubarb or spinach.

Accordingly, in a first aspect the present invention consists in a process for removing calcium oxalate from 35 plant tissue comprising forming the plant tissue into a ' ' 199/,;; fluid stream, subjecting the fluid stream to a separation process to form a calcium oxalate rich fraction and a substantially calcium oxalate free fluid stream and recovering the substantially oxalate free fluid stream.

In a second aspect the present invention consists in a processed food product which includes a plant tissue extract substantially free of calcium oxalate and/or oxalates characterised in that the plant tissue in its native state contains calcium oxalate and/or oxalates. 10 In a preferred embodiment of the present invention the plant tissue is kiwifruit.

In a further preferred embodiment of the present invention the plant tissue is generated by mechanical separation of chlorophyll from plant material. 15 In yet a further preferred embodiment of the present invention the fluid stream is treated with a soluble calcium salt to precipitate oxalates present in the fluid stream as calcium oxalate.

In yet a further preferred embodiment of the present 20 invention the separation is accomplished by centrifugation.

In yet a further preferred embodiment of the present invention the plant tissue is formed into a fluid stream by crushing or grinding and/or mixing with water.

In a typical application food is made into a liquid 25 stream either by crushing or grinding and/or then mixing with water as necessary. The resulting stream is passed through a centrifuge or similar apparatus such that the heavier oxalate crystals are retained in the apparatus or ejected in a crystal-containing stream. The liquid stream 30 has substantially reduced oxalate levels.

Therefore a typical application in kiwifruit is to remove the crystals from the pulped fruit to eliminate the "catch-in - throat" sensation that occurs when foods made from the pulp are consumed. Another application is to 35 remove oxalate crystals from liquid streams that contain chlorophyll such as would be generated in the mechanical separation of chlorophyll from plant tissue.

Such streams are likely to contain oxalates as they are part of the same biochemical process and since the 5 oxalates are denser than the chlorophyl1 containing tissues separation can be readily achieved.

Detailed Disclosure of the Present Invention In order that the nature of the present invention may be mo re clearly understood, preferred forms thereof will 10 now be described with reference to the following examples.

Example 1 A raphide free juice was made by placing lOmL of diluted kiwifruit juice into a centrifuge tube and spinning the tube at 2000rpm in a laboratory centrifuge. 15 After 15min the juice had no needles present and the lower section of the retentate could be isolated into two separate fractions. The upper fraction contained about 1mm of a rich green chlorophyll fraction. The lower fraction contained the calcium oxalate raphides with a 20 small amount of chlorophyll present.

Examole 2 A raphide free juice and a chloroplast fraction with substantially lower number of raphides was made by the following procedure: 20kg of kiwifruit were pulped in a hammec mill.

Seeds and skin were removed in a brush finisher. The resulting juice was diluted with water 1:1 and passed through two screens with 150um and 50um openings respectively. The screens removed the larger fractions of 30 fruit tissue and some but not all of the raphides.

The juice was then passed through a centrifuge where four distinct fractions were discerned. A juice fraction essentially free of raphides, a green fraction of chloroplasts containing about 2 x 10^ raphides per gram, 35 a brown fraction which contained 138 x 10^ raphides per ^ ocr799;.. ,<s - o - gram and a white paste fraction at the spindle of the centrifuge which contained 219 x 10® raphides per gram. Although the green chloroplast fraction contained raphides the number was substantially lower than would be expected 5 to give a "catch - in-throat" in products made using the chloroplasts for making recombined kiwifruit products. Further centrifugation of the resuspended chloroplast fraction showed further separation of raphides from the chloroplasts.

Example 3 A liquid stream of reduced oxalate content was obtained using a hydroclone centrifugal device to treat kiwifruit juice diluted to 0.6° Brix. The hydroclone separated the juice into two streams in the upper stream 15 the number of needles was up to 59% lower than in the lower stream. The flow rates of both streams were similar at about 2kg.min'^ and the lower stream had .195 x 10® raphides per gram and the upper stream had .078 x 10® raphides per gram.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments 25 are, therefore, to be considered in all respects as illustrative and not restrictive.

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Claims (10)

WHAT WE CLAIM IS:

1. A process for removing calcium oxalate from plant tissue comprising forming the plant tissue into a fluid stream, subjecting the fluid stream to a separation 5 process to form a calcium oxalate-rich fraction and a substantially calcium oxalate free fluid stream and recovering the substantially oxalate-free fluid stream.

2. A process as claimed in claim 1 in which the plant tissue is kiwifruit. 10

3. A process as claimed in claim ) in which the plane tissue is generated by mechanical separation of chlorophyll from plant material.

4. A process as claimed in claim 1 in which the fluid stream is treated with a soluble calcium salt to precipitate oxalate 15 present in the fluid stream as calcium oxalate.

5. A process as claimed in any one of claims 1 to 4 in which the separation is accomplished by centrifugation.

6. A process as claimed in any one of claims 1 to 5 in which the plant tissue is formed into a fluid stream by crushing or 20 grinding and/or mixing with water.

7. A food product substantially free from calcium oxalate or oxalates, the food being subjected to the process as claimed in any one of claims 1 to 6.

8. A process substantially as hereinbefore described 25 with reference to any one of Examples 1 to 3.

9. A processed food product which includes plant tissue substantially freed of calcium oxalate and/or oxalates by a process as claimed in any one of claims 1 to 6 or 8. 30

10. A processed food product as claimed in claim 9 in which the plant tissue is kiwifruit. WEST-WALKER, McCABE per: attorn-.-.- applicant