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Developments in citrus products

Mark Harrison

Technical Manager-Processing, Leeton Juices. Leeton. NSW

The Australian citrus industry is centred on the irrigation areas of the Murray and Murrumbidgee River systems. Citrus in Australia is produced several hundred kilometres away from the coast in a dry Mediterranean climate on ancient alluvial soils and being entirely dependent on irrigation to survive. This is uncharacteristic of the world scene where citrus production is usually coastal, has been non-irrigated and is produced on younger soils. The fruit hectarage in Australia has been increasing in recent years with the initial expansion being in processing fruit with, more recently, fresh eating fruit varieties (navels) being planted. The fruit quality in the citrus industry has been to date (fortunately for the juice processing industries) based on the highest quality juicing orange, the Valencia. This has led to a concentration of supply of fruit tonnage being presented for processing around the months of December to February, while fruit is available for at least ten months of the year. This high concentration of fruit receivals has meant considerable effort has been expended in high volume juicing plants using technologies developed in the fifties with some adaptation since then, but no real changes until recently.

The citrus industry has a lot in common with the grape and wine industry in the desire to provide both fresh fruit and to process fruit. This fruit is processed to a palatable juice of the highest quality as soon as possible after harvest with the minimum amount of interference by us, the processor. This is the ultimate goal of all citrus processors, as I hope it is of all food processors. The citrus industry has yet to completely achieve this goal.

There has been a recent swing to "fresh" products which have undergone the least amount of processing, are "safe" (generally meaning no chemical additives) and which are convenient to use. The use of processing techniques which may have been acceptable just a few years ago are now seen as less acceptable or even optional by many. This is the challenge that we all face, to maintain our record of hygiene and consumer safety while still presenting our customers with the product they perceive as good and is good for them. With the help of organisations such as the CSIRO and various State, Federal and other agencies, answers to the question of "where do we go from here?" will be forthcoming.

There have been several developments in the production and processing of citrus products which have emanated from the CSIRO Division of Food Processing in the recent past and I will quickly recap some of these.

The spinning cone column for the removal and separating of volatile components from a base product such as fruit juice or wine. The commercial realisation of this process has yet to be a success in our industry, due in no small part to conservative thinking with regard to the new products produced.

The adaption of the counter current extractor (CCE) with the innovation of the automatic reversing of the main screw. This enables a more efficient extraction of soluble solids to occur. The main drawback of this process is in its use to extract soluble solids from non-traditional sources such as pineapple skins, apple cores and citrus skins. The innovation of increased yield has been met with considerable bureaucratic resistance and to this day the process lies between legality and prosecution.

The use of polymeric absorbent resins to reduce various undesirable components of citrus fruits. This includes acid reduction (deacidification), limonin removal (debittering), mineral adsorption and various other component adjustments of citrus juices. This process is used in conjunction with the CCE process to ameliorate the properties of the extracted solids to make a more desirable product.

There are several areas of interest being investigated in various parts of the CSIRO which I will not try and cover exhaustively, but will mention a number.

The development of new techniques to extract difficult products from fruit, a good example of which is the recent development in Kiwi fruit extraction with the maintenance of the green colour.

The development in Australia of a novel membrane concentration method known as Osmotic Concentration in which no heat is involved as well as low pressure differential (unlike reverse osmosis) so avoiding the changes to delicate flavours brought about by both heat and pressure. This technique is one of the most exciting things to happen in our industry in 40 years. The work is being helped along by Dr Xian Jiang and Michael Rooney.

Recent developments in the extraction of soluble solids from peel have meant that the regulatory authorities need to be able to monitor these new techniques. This has led to a project to find a method of detection for peel extracts, which is a novel way of ensuring work, i.e. develop a new extraction technique and then develop a technique of monitoring the new process, hopefully not to prevent its use!

With the recent push towards "fresh" there is increasing interest in understanding the intrinsic flavours that are essential for this fresh flavour. There is need to use people such as Dr Frank Whitfield at the Centre for Advanced Micro Analysis of Food, and others involved in flavour evaluation.

One of the most controversial and evocative subjects has not had much airing, and that is the investigation of the effects of various extraction methods on pesticide and microbial residues in final products. This overlaps with the use of techniques such as pasteurisation and chemical washing of fruit to reduce microbial loading in the highly mechanised plants of today. My own personal worry is that in the drive by marketers to become holy and natural the safety that today's consumers have come to expect will not be sacrificed. This would lead to far more deadly problems than the processes they are replacing.

The development of satisfactory and environmentally safe methods of disposal or use of effluent from citrus plants. The main worry at present is the potential of citrus oils to flush through the system with their known bactericidal properties. This is a major worry thoughout the world's citrus industry.

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