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by Mr M.J. Gregory and Professor R.C. Menary,
School of Agricultural Science and the Tasmanian Institute of Agricultural Research - University of Tasmania.
October 2007
RIRDC Publication No 07/141 RIRDC Project No UT-39A
Executive Summary
What the report is about
This report describes research
conducted for the purposes of:
Who the report is
targeted at
This project was initiated
and supported by Tas-Saff Pty. Ltd., the only significant producer of saffron
in Australia. The findings in this report are therefore primarily targeted
at Tas-Saff and the growers contracted to them.
Background
Saffron is produced from
the careful separation and drying of the stigmas from the flowers of Crocus
sativus and is (w/w) the world’s most valuable culinary spice. It is also
currently receiving renewed worldwide interest for its medicinal properties.
Saffron has traditionally been used in Chinese medicine, and is now the subject of scientific research for its use in anti-cancer, anti-inflammatory, anti-depression and pro-memory/learning treatments.
Some of this work has reached the clinical trial stage. At present the cost of saffron spice is prohibitive to its use as a drug but the potential world market growth for saffron based products in coming years is clear.
The presence of colchicine – a compound used commercially as a drug to treat gout and in plant genetics – has also been reported in the corms (bulbs) of Crocus.
Australia imports approximately 800Kg of saffron annually at a value of $14m. Tas-Saff is the first and only significant commercial producer of saffron in Australia. The growth of the local industry has been restricted by the labour intensive nature of the harvesting and post-harvest processing procedures and competition with imports from countries with much lower labour costs. The local industry has therefore identified the need to gain market advantage over imports through optimisation of saffron quality.
This report details a research
project aimed at providing the analytical assessment of the quality and
consistency of spice product from the Australian saffron growers in relation
to world standards and determination of:
These aims were more
specifically detailed through the following objectives.
Objectives
These combined objectives
were aimed at facilitating the growth of the local industry by providing
the means to gain market advantage through improved quality of the current
product – and to allow value adding through new products from the saffron
crop.
Methods used
Application of International
Standards Organisation (ISO) testing procedures and comparisons with other
analytical extraction and chromatographic techniques were used to compare
the local product to the ISO standard and competitor’s imported products.
Comparisons were also made between individual Australian grower’s samples
to gauge the range and consistency of quality within the local industry.
Application of different conditions using commercial food dryers, ovens and then a purpose built apparatus were applied to stigmas for drying experiments during the 2004 harvest period. A purpose built drying apparatus was designed and constructed to better study these conditions during the 2005 harvest. Application of the same analytical techniques described above, were used to measure quality parameters in both years and then to apply these findings to commercial scale drying during the 2006 harvest. Further to this an investigation of the effect of applied humidity and thus manipulation of the water activity of the stigmas during drying was completed during this 3rd harvest.
Waste flowers, with or without rejected stigmas, were collected during the harvest periods for distillation and extraction trials with some processed then and the remainder frozen for later work. A variety of different post harvest treatments were applied to both fresh and frozen flowers that were then either hydro-distilled or solvent extracted. Products were assessed organoleptically and by chromatographic analysis.
Extractions of Crocus corms were performed at intervals over the dormancy period and analysed chromatographically for identification of any colchicine content.
Results and findings
ISO and analytical testing
of quality parameters Full ISO testing procedures showed that local samples
of saffron selected for sale from the 2003 harvest met all criteria for
ISO, category 1 product, but that potential for significant aroma improvement
existed. Samples of competitor’s imported products fell short of the standard
for the colour and bitterness measurements.
Individual grower samples from 2003 and 2004 were tested 6 months after harvest and 2 of these were retested again after 12 months extra storage. It was revealed that most (90%) of the samples had moisture samples above the 12% standard with a significant number (30%) more than 5% over this, indicating that a significant problem with insufficient drying was occurring.
For the key colour, bitterness and aroma strength measurements 15% of the samples were deficient (for ISO standard) in the former 2 properties, as well as both those re-tested after a further12 months.
Storage with excessive moisture leaves the saffron prone to enzymatic degradation of the colour components and this was apparent from the re-tested samples, though colour loss can also occur prior to or during the drying process.
Comparison of the grower samples to a variety of imported products showed that while the local saffron generally compared well for colour to those from Iran and an Italian sample, the latter products had higher aroma strength measurements, except where the local products had greatly degraded in colour. None of these samples compared well with an analysis of the Spanish product (from the region renowned having the world’s best saffron) that had both high aroma and colour. The differences were even greater when results for solvent extraction and GC measurement of the aroma compound, safranal were compared as an alternative to the ISO test. The Spanish sample had at least twice the safranal content of all other samples and 3-8 times the content all those where colour was not low. It also had colour strength higher than all other samples. This analysis suggested that for the local product, considerable improvement in the aroma content should be possible, without excessive colour loss.
It was shown that the ISO test procedure for aroma strength correlated very poorly with (non-polar) extraction and analytical GC analysis. The failure of the ISO method to reflect large differences in safranal content is consistent with the recent observations of several other authors – and so for all later work the analytical method was used.
Drying experiments The stigma drying experiments conducted during the 2004 and 2005 harvest indicated that high temperature drying procedures could enhance aroma formation. Highly significant increases in safranal content were achieved when compared to lower temperature ranges (used currently by the local industry) and with improved colour retention. There was also evidence that the use of significant air-flow; an integral and unavoidable aspect of the use of the current commercial apparatus/method, causes significant loss of safranal.
In response to these results, and the difficulty encountered with the use of conventional ovens in accurately applying precise high temperatures for the relatively short periods required, a purpose built apparatus was designed and constructed to allow proper isolation of the effects of different conditions by using the same device for all treatments. It also served as a prototype for a potential new commercial dryer. This device incorporated heating via blacked out conventional light bulbs controlled by a PID temperature controller, a cylindrical aluminium structure to reduce thermal inertia and a fan with speed control.
The prototype dryer was successfully used for a series of stigma drying experiments during the 2005 harvest. The results indicated that at the elevated temperatures, significantly more safranal was generated and colour components retained, than at lower temperatures. Drying at high temperature for approximately 25 minutes gave the highest result with an 8-10 fold increase in safranal content over the lower temperature treatment currently used by the industry. Furthermore, it was confirmed that the use of air-flow causes reduced safranal levels, probably due to evaporative loss, and that this effect was significant even at relatively low airspeeds. This air-flow effect occurred at both high and low temperatures, although it was more pronounced at the former.
In critically assessing the new drying apparatus it was found that, while it worked well for the experiments undertaken, for commercial use major adaptations were required to incorporate a capacity for greater volumes of stigmas while limiting the number of drying levels to minimize temperature variations throughout. To this end it was planned to design a new device with a flatter, rectangular shape and side access to allow rapid and easy sample introduction and removal and to test this apparatus during the 2006 harvest. Before this was attempted however, the following findings shed new light on the requirements for this device.
Although not originally planned as one of the described tasks, an investigation of the importance of water activity to safranal production in the drying process was undertaken during the 2006 harvest.
This work was begun as part of an ensuing PhD project, but the initial results are included here because of the important implications regarding the optimal drying procedure.
It was shown that by using a container of hot water in an enclosed (but non-pressurised) drying apparatus (oven) set at a specific high temperature to achieve an equilibrated relative humidity (RH) of approximately 50%, the drying rate of the stigmas was significantly slowed. Although seemingly counter-intuitive for a drying process, this actually allowed the stigmas to remain for longer within a critical range of water activity. As the stigma temperature was sufficiently high this allowed significantly greater (x3) hydrolysis of picrocrocin to form safranal when compared to the optimum high temperature treatments (without applied humidity) identified earlier. The colour strength of the saffron produced in this way was also enhanced.
Colchicine assay LC-MS/MS analysis of broad-spectrum methanol extracts of Crocus corms at intervals over the 2003/04 summer dormancy period failed to detect any colchicine. The relatively crude isolation method employed meant that very low concentrations of colchicines or related compounds could have been missed, but in such a case commercial extraction of these would not be viable and so this part of the project was discontinued.
Waste flower products None of the distillation products from waste flower samples was obtained in sufficient yield (all < 0.1%) to make this type of product potentially viable. It was noted that the best distillation products contained safranal and this was only obtained from flowers containing some reject stigmas.
Application of extraction trials confirmed that safranal was only generated in samples containing some proportion of reject stigmas indicating that its precursor does not occur in the petals or stamens.
Products obtained from flowers without stigmas, although of pleasant aroma and attractive bright orange red colour, did not have the aroma impact for a potential fragrance product. The stigma content (w/w) of all later waste flower samples obtained from growers was therefore determined. The average content of stigmas for sample obtained from the 2004/05 harvests was found to be 0.35% by weight.
Trials of different pre-extraction treatments on fresh and frozen flowers combined with organoleptic assessment revealed that the best product was obtained from fresh flowers dried slowly at ambient temperature for 3 days in the dark. This extract was also shown to have the highest yield of safranal per unit wt. of stigmas. Drying of flowers at higher temperatures also resulted in a loss of other nonsafranal aroma notes.
A trial of farm scale collection and onsite drying of waste flowers during the 2006 harvest period revealed that air drying of these flowers on horizontal mesh nets in sheds away from direct sunlight was feasible, though slow in poor weather conditions. An alternative to this method was the use of the food dryers at low temperature (30ºC) though this did result in some loss of volatiles including safranal in the extract and involves considerably more of the grower’s time to perform. This loss of volatiles may not be critical if reject saffron is used to augment the extract.
Extraction with a solvent mixture of 10% ethanol in hexane gave a higher yield of product (5%) than extraction with 100% hexane (2%), but the latter had a more attractive colour and persistent aroma.
This sample was selected for independent expert assessment by a leading international perfumer. The feedback from this was very positive with the following quote summing up the potential: “Market potential- small and niche. 'People would bite your hand off if it was the right price and available in quantity'. Price suggestion: several hundred £/kg would guarantee a market”.
At present there is insufficient weight of saffron flowers produced by the local industry to create a viable market for the extract described above. However, the use of a currently existing stock (of many 100g) of reject saffron (with degraded colour) could be used to greatly strengthen the safranal aroma impact of the product. This and the clearer identification of extract components with established health care properties (of which safranal is one) could attract a much higher price.
The establishment of a small market for a new product such as this could then encourage a more rapid increase in the Crocus crop production than has been occurring in recent years. This would allow the extract to be produced in quantities more suitable for potential buyers and part of the crop could be used exclusively for this production ensuring that the high safranal content of the product was maintained.
The other potential means of boosting the safranal content would be to further investigate the chemistry of the safranal conversion from its precursor picrocrocin. The analysis of samples from the drying experiments revealed that even in those samples with the highest safranal contents, there remained a 25-50 fold excess of the precursor. Thus, there is a great potential for very considerable safranal yield gains given the right post harvest treatments and this could lead to an extract product with boosted aroma impact from only a small stigma content such as used in these trials.
Reports in the literature indicate that saffron flowers contain significant contents of glycosidically bound (and therefore water soluble and non- volatile) carotenoids and other potential volatile/aroma compounds. Fermentation treatments such as those used to boost the aroma in products such as tea, tobacco, rose oil and Boronia, could potentially be used to cleave off the sugar unit from these molecules in preparations of Crocus flowers to release new aroma volatiles and improve the yield and fragrance strength of extracts.
Implications
Saffron quality
Drying methods
The findings of this study
show that, given the application of appropriate drying methodology, the
quality of Australian saffron can and should be significantly improved.
Most of this improvement will come from increased aroma production, but
high temperature/humidity drying will also have a preserving effect on
the pigment content as enzymatic degradation is prevented. This should
result in consistently higher colour strengths that would be maintained
in storage.
The saffron filaments produced from this process tend to be too dry and brittle for easy packaging but in the laboratory some moisture, and with it, much of the resilience is returned by equilibrating the filaments at ambient temperature in a darkened room – possibly with a warm container of water nearby to provide a slightly higher localised atmospheric humidity. This equilibration was shown to work well on a commercial scale although some variation with weather conditions (and thus ambient humidity) did have an effect and would need to be taken into account in timing the length of equilibration. The use of a high humidity drying method may decrease the need for this equilibration.
The implementation of the new drying method would best be made using an apparatus such as an oven or incubator that is enclosed so that a high relative humidity can be uniformly achieved within by simply introducing a dish of hot water. The inclusion of precise temperature control (such as PID) would be an advantage and the device should be calibrated with for the temperature settings when used with added moisture in this way. The method has worked well with an oven of 24L capacity and while a larger chamber would be good for increasing the number of stigmas that may be dried per run, if it is too large, uniformity of temperature and humidity will be more difficult to achieve.
Competition and growth of the industry The local saffron industry is competing with products from countries with considerably lowers labour costs. In this situation there are 2 alternative ways of providing competitive advantage; reducing the local labour costs or producing product that is demonstrably superior in quality and therefore can attract a higher price. The only way that the former could be achieved in Australia would be through the successful implementation of mechanical flower harvesting and stigma separation.
Some documented attempts have been made to design equipment to mechanise the cutting and collection of flowers, particularly in Italy(1) but the results tended to result in excessive loss of flowers, increase impurities and have negative effects on eventual saffron quality. All the methods tried also tended to cut a considerable proportion of the leaves surrounding the emergent flowers which compromises the later growth of the corms resulting in poor flower yields in subsequent seasons.
Saffron flowering also occurs randomly through a crop over several weeks so that flowers need to be harvested on virtually every day over that period with considerable judgement applied to pick flowers at the right stage of maturity. Any successful mechanical system would require much more uniform flowering to accomplish significant labour saving. This would probably require hormonal and/or environmental manipulation of the plants. One reference was found describing work relating to the hormonal application(2) but at this stage not enough is known about Crocus physiology to achieve uniformity of flowering this way. Recent trials of indoor (glasshouse) environmental control of saffron crops has shown that flowering timing can be controlled to a degree and product yields potentially improved through more reliable flowering, but no improvement in flowering uniformity was described(3). Glasshouse based environmental control may be a more efficient method of producing high yielding quality saffron but considerably more research would be required to establish the precise methods for this as well the cost benefits as this form of horticulture is much more capital intensive than the current practises.
Even supposing that mechanical harvesting of a uniform flowering crop could be achieved then that would place considerable pressure on the stigma separation and drying facilities, as the yield of flowers currently processed over several weeks would need to be processed at once. Separation of stigmas from other flower parts was also attempted in the Italian studies(1) by means of fans and wind tunnels but these were not successful because the connection between the base of the style (stigmas) and the other flower parts which tended to remain intact and because the petals tended to wrap around the stigmas unless the flower was totally open and beyond the optimal harvest stage so that quality was compromised. The process also tended to prematurely dry the flowers and result in loss of aroma.
In searching for any information on mechanical harvesting, 2 Indian websites(4;5) were found claiming that mechanised systems for saffron harvest, separation and drying had been developed.
Attempts to contact the organisation responsible have been unsuccessful to date. There is thus no information available at present on the means of mechanisation or quality of the product from these systems. All the saffron produced in India is for the domestic market in that country and does not have a reputation for high quality(6).
Mechanisation of the harvesting separation process may well be feasible, but significant research effort (with a new set of objectives to those investigated here) would first be required to solve all the significant problems associated with the growth and flowering of Crocus without compromising saffron quality. This would require considerable financial input from an industry that has not yet reached the stage of development to justify investment of that scale.
In contrast, the present study has shown that the aroma and colour characteristics of the local product can be (with the appropriate drying technology) significantly and consistently improved, potentially to a quality level that is superior to saffron from competitors anywhere else in the world. If this allows the local Industry to grow through the capture of a larger proportion of the domestic market as well as export developments, then this would be the first step towards establishing the resources to properly investigate mechanical harvesting and processing and alternative ways of growing the crop.
New products This study has shown that commercially attractive extract product(s) for use as a fragrance can be obtained from the waste flowers as long as those flowers contain at least a small % of stigmas. This has been shown to occur during the normal course of harvesting as stigmas are missed or rejected due to visual defects, but it is possible that the extraction could also be augmented by addition of saffron rejected for sale (due to colour loss) that adds to the aroma (and health care) properties of the product.
In the long term, to properly establish a market for a fragrance product, the overall volume of Crocus crop would need to increase significantly to provide sufficient product for buyers. The economic viability of growing some proportion of the crop just for extraction should be assessed, but first more work is required to chemically characterize the extract produced. This should include investigation of the content of components with medicinal/health care properties as well as the best methods of post harvest treatments to optimise these properties and the overall yield.
The encouragement of the growth of the local industry through quality improvement and development of new product(s) with a continuation of the investigative study of the underlying biochemistry, will better position the local saffron industry to take advantage of future trends in international demand for saffron products as the healthcare/medicinal properties of the spice become more commercially utilised.
Recommendations
1. Saffron production from
the drying of stigmas should be facilitated by applying high temperature
in an elevated humidity without applied air-flow.
2. For this drying it is
recommended that growers obtain suitable ovens or incubators that may be
adapted to suit drying conditions, or to design and construct a saffron
specific apparatus with the following features:
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