Organisation: Food and Agriculture Organization of the United Nations (FAO), AGST
Prepared by Anne Plotto.
Edited by François Mazaud, Alexandra Röttger, Katja Steffel, Larissa D'Aquilio (HTML transfer)

CHAPTER XXIX TURMERIC: Post-Production Management for Improved Market Access for Herbs and Spices - Turmeric

3. Proposed improvements
3.1 Cultivar
3.2 Post-harvest handling
3.3 Storage

3. Proposed improvements
3.1 Cultivar

In India, the region of production determines the name of the type of turmeric. Although the average productivity of cultivated turmeric remains at an average low, breeding for crop improvement is difficult due to plant sterility.¹⁹ The Indian Institute of Spice Research in Calicut, Kerala, has however proceeded to crop improvement by clonal selection. This Institute currently maintains a collection of 500-600 accessions of turmeric, all named for the distinct locations from which each was collected.¹⁹ Other institutions are also proceeding towards a similar effort, observing production yields and qualities of turmeric collected from the Tarai area of Northern India transplanted under plain conditions.²⁴ The following Indian cultivars were released by the Indian Institute of Spice Research.

Table 10: Indian cultivars released by the Indian Institute of Spice Research ^{3, 10, 41}

^a: First value is observed yield, second value is potential yield
Source: http://www.iisr.org/varieties/

3.2 Post harvest handling

It is recommended that washed rhizomes be dried as soon as possible to minimize contamination, mold growth and fermentation. Boiling the turmeric rhizome in the curing process significantly reduces the microbial load on the rhizomes²⁶. If the rhizome is additionally dried in a mechanical drier, the potential for dust contamination is lessened. After drying, specific equipment is suggested for optimum cleaning of the dried rhizomes⁴³: a plain sifter and an air screen separator will help remove small materials such as dead insects, excreta and extraneous matter, while a rotary knife cutter, a screen separator and a de-stoner will help remove residual insects and other extraneous matter.

In spite of the curing and drying process, turmeric still carries a heavy bacterial load³³. Specifically, toxigenic molds are reported on turmeric and other spices. Among the post-processing disinfection treatments available for spices, ethylene oxide is currently approved for use on spices in the United States with a maximum residue of 50 ppm after treatment.⁵³ However, ethylene oxide is dangerous to apply, and highly carcinogenic by inhalation. It has to be applied in specially-built facilities. The use of ethylene oxide is banned in the European Union and in Japan.¹⁷ The U.S. Environmental Protection Agency (EPA) has a maximum tolerance residue for ethylene oxide of 50 ppm on spices (40 CFR, 180.151). Propylene oxide is an alternative to ethylene oxide, but is not as efficient.⁵³ If ethylene oxide is withdrawn form the market, it is likely that propylene oxide will follow the same route.

Irradiation is becoming an increasingly accepted technique to sterilize spices and other food products, mostly meat products and fruits.³³ It too requires specially built and secure facilities. The common dose applied to spices is 3 to 10 kGy. By law, a spice irradiated once cannot be irradiated a second time; therefore, bulk irradiated spices must be well labelled to avoid a second irradiation if it enters as an ingredient in a meat or other product that will be irradiated.⁵³ Irradiation of turmeric rhizomes with 10 kGy at a dose rate of 19 Gy·min-1 was reported not to modify the composition of volatile oils extracted after one week of storage at 5 ºC.17 The antioxidant activity as measured by the protective ability of linoleic acid oxidation (thiobarbituric acid value and peroxide value) was also reported to be unaffected by irradiation.¹⁷ Laws allowing irradiation on foods vary greatly by country within the European Union. Several test methods are available to detect whether a spice has been irradiated. One method is based on the observation that irradiated spices exhibit thermoluminescence. However, it appears that inorganic dust present in spice powders have the highest thermoluminescence capacity from irradiation. Therefore, one study suggested that salt (NaCl) could be added before irradiation and serve as an indicator for irradiation.¹⁴ This may not be very practical for all spices. Other reported methods include electron spin resonance spectroscopy.^33,53

3.3 Storage

Turmeric pigment is highly unstable as compared to the yellow synthetic colorant, tartrazine.¹⁵ However, if protected from light and humidity, the curcuminoid pigments in turmeric powder and oleoresin are stable. Therefore, turmeric rhizomes and powder should be stored away from light and in a very dry environment.⁴³ Additionally, all water or ethanol solvent should be removed from the oleoresin to assure pigment stability.¹⁵