Near infra-red (NIR) spectroscopy

What is NIR ? Near infra-red (NIR) spectroscopy is a technology that has vast applications in agriculture. Near infra-red is a small part of the spectrum of light ( nm). VISIBLE (400–700 nm) At one end of this spectrum are the high energy waves such as x-rays and ultraviolet, while at the other end of the spectrum are the low energy waves such as infra- red, micro waves and radio waves. Near infra-red is a part of natural sunlight and is generated by several light sources, such as tungsten halogen car driving lights. Near infra-red is between the visible and the infra-red.

The colour of e.g. an apple in the visible spectrum gives us information on a variety of pigments and chemicals in the fruit, but we can not ‘see’ things that do not absorb visible light (e.g. a sugar solution). It happens that water, sugar, acids and a range of other organic substances absorb near infra-red in proportion to their concentration. Spectroscopy is rapid, timely, less expensive, non-destructive, straightforward and sometimes more accurate than conventional analysis

Near infra-red spectroscopy (NIRS) has been in routine use for the assessment of a range of components in dry materials (e.g. protein in grains). The presence of water, which also absorbs strongly in the near infra-red has limited the use of NIRS for assessment of quality of fresh produce. However, recent improvements, namely, the massive increase in computing power of modern PCs and the development of software capable of carrying out the complex statistical mathematics has made the technique applicable to high moisture products such as fresh fruit.

Limitations of NIR Technology The most important limitation of the technology lies in the development of calibrations. Perhaps these can be explained by analogy with the N content of a leaf. You expect a leaf with a higher nitrogen content to be ‘greener’, but you know you can not say that a sugar cane and a corn leaf with the same level of ‘greenness’ have the same nitrogen content. In other words, different calibrations apply. Thus the NIRS technique is not so much hardware limited as ‘software’ or calibration limited. Ultimately, it will be the cost of calibration maintenance that will make or break commercial adoption in the world.

The NIRS technology can be applied to the sorting of fruit at commercial packline speeds. Indeed, it is in commercial use in Japan, primarily for melons and citrus fruit. The Japanese firms are currently marketing NIR based sorting and grading systems for use with citrus, pome fruits and stone fruits in Japan. It is perhaps not surprising that the technology has been applied quickly in Japan, where fruit are with huge price (single melons selling for routinely at $30). However, with modification and reduction of price, the technology is applicable to markets with less reward for premium quality. NIR agricultural applications

The development of a high speed system incorporated into a packing line would enable the sorting of fruit based on quality parameters such dry matter content. The technology may be used to exclude fruit with internal defects. A portable unit would enable random checks of fruit in the field, or in the wholesale or retail store. On-harvester estimation of grain protein content for precision agriculture and estimation of the sugar content of fibrated sugar cane (beet) in sugar mills. In the future, we should expect to see the application of NIR technology to assessing a range of food products for various aspects of quality and safety.

Commodity areas and possible NIR applications that have been investigated are: Coffee - taint analysis Sweet Corn - insect damage and insect detection Coal - moisture determination Macadamia kernel - quality Citrus - quality attributes Pineapples, mango's, strawberries - quality attributes Stone fruit - quality attributes Melons - quality attributes

MIR Technology (Mid Infrared Spectroscopy ) This technology can provide good quality prediction of soil properties, eg, carbonate and organic carbon, total nitrogen, cation exchange capacity and some exchangeable cations, electrical conductivity, pH, soil texture and a number of other properties, some of which are expensive to measure by conventional methods and not usually available. MIR analysis of soils is seen as a technology for the future, with applications that augment conventional soil testing and decision support, and capable of measurement in the field. MIR (2500–25,000 nm)

MIR vs NIR Near infrared reflectance (NIR) spectroscopy, which is a similar approach but uses a shorter wavelength band than MIR, has been used for analysis of minerals, forages, plant material and grains as well as for some soil materials For prediction of soil properties, found MIR superior for several reasons, although NIR has been shown to be very useful. Technically, NIR relies on part of the spectrum that contains weak overtone and combination spectral frequencies that can be observed better as intense, fundamental vibrations in the MIR range. NIR is insensitive to quartz, a major component of most soils. However, NIR is well supported commercially, is well suited to field portability, remote sensing, copes better with moist samples and can deal with larger bulk soil samples because of its more intense sources and sensitive detectors.

MIR applications soil analysis, decision support, soil property classification, soil survey and mapping, precision agriculture, diagnosis of soil problems, contaminated site characterisation and management

MIR application for fruit bruising NIR application for agriculture