Nondestructive Detection of Fruit Fly Eggs and Larvae in Mango
by Near Infrared Spectroscopy
S. Saranwong,1 N. Suttiwijitpukdee,2 S. Kasemsumran,2 W. Thanapase2 and S. Kawano1
1National Food Research Institute, Tsukuba 305-8642 Japan, E-mail: sirinnap@affrc.go.jp
Kasetsart Agricultural and Agro-Industrial Product Improvement Institute (KAPI), Kasetsart University,
Bangkok 10300 Thailand

2Regression coefficient[Introduction] Fruit fly is one of the important pests from the point of plant quarantine. In order to prevent thespreading of fruit flies from South East Asia to Japan, tropical fruits that may be the host of this insect should be
disinfected by vapour heat treatment. However, the vapour heat treatment can cause quality deterioration in fruit
at some extents. In this study, in order to maintain the quality of exported fruits, near infrared (NIR)
spectroscopy had been examined for its potential to classify fruit fly infested mangoes from the clean ones.
[Materials and Methods] One hundred and two green mangoes were used; 92 sampleswere used as control
while another 92 samples were used as infested samples. At first, nine pores with 2 mm depth were made on thefruit shoulder in the area of 1 cm2 using a sterile sewing needle. The artificial infestation was done by placing thepored fruit in a fruit fly cage for 30 minutes. NIR measurement was performed with the FQA-NIR Gun(Shizuoka Shibuya Seiki, Hamamatsu, Japan) in the short wavelength region (588-1092 nm) using theInteractance mode (Figure 1). The measurements were performed at 0, 24, 36 and 48 hours after infestation.
Prior to NIR measurement, sample temperature was controlled by dipping the fruits into 25°C water bath for 15minutes. A polyethylene sheet was used to cover the surface of water to prevent the fruits from getting wet.
Data analysis was carried out using “The Unscrambler” software (CAMO, Oslo, Norway). Second derivative
spectra (Savitzky-Golay algorithm, left and right averaging of 28 nm and 2nd order polynomial) were used.
Partial least square (PLS) regression was used to predict the classification value of “0” (control group) and “1”(infested group). Validation was performed by leave-one-out full cross validation.
[Results and Discussion] Visually, there were no differences between second derivative spectra of control andinfested mangoes. By the effect of water absorption, neither fat band nor protein band due to the present of fruit
fly eggs could be observed in the NIR spectra of forced infested mango. Using PLS regression, the results shownin Table 1 could be obtained. It was found that the classification performed at 48 hours after infestation could
provide satisfied results with only 2 false negatives of a total of 48 samples (4.3 %). The regression coefficientplots indicated that the absorption due to in the vicinity of 730 nm had an important role on the classification(Figure 2). The peak was considered to be the protein absorption band of fruit fly larvae, for only the dried fruit
fly larvae absorbed the NIR radiation in this region.
5000
4000
3000
2000
1000
0-1000
-2000
-3000
-4000
-5000
-6000

48 hr

856
781

750

908
919

728

700

Figure 1. NIR measurement of mango

36 hr
24 hr
0 hr

800
850
wavelength (nm)

900

950

Figure 2. Regression coefficient plots.

Table 1. PLS classification results calculated from second derivative NIR spectra.
Number of fruits
Period after
WavelengthFInfested
infestion(nm)Correct
False
SD
Correct
00 hr
700-950659370.28
7424 hr
700-950789
70.26
9336 hr
700-950786
100.269348 hr
700-950
790
60.26
95
SD: Standard deviation of NIR-predicted value

Control
False
223
31SD
0.17
0.20
0.19
0.16