Visible-Light Spectroscopy and Laser Scattering for Screening Brewed Coffee Types Using a Low-Cost Portable Platform

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This work presentes an innovative low-cost platform, but current dataset and analysis are exploratory. Manuscript requires softening in the claimed practical value, or otherwise substantial methodological strengthening before the approach can be considered a reliable analytical tool for coffee-quality screening.

1. All optical indicators remain semi-quantitative without calibration against an accepted metric. Manuscript states “multivariate analysis successfully differentiate the drinks” - but overall I would not agree with this. It is an interesting and original work, but remains mostly semi-quantiative and explroatory.

2. White-light data are fitted with a dual-region exponential (Beer‐Lambert predicts linear absorbance vs concentration for homogeneous solutions). Offset term y(lambda) lacks physical justification.

 

Author Response

Comments and Suggestions το Authors

This work presents an innovative low-cost platform, but current dataset and analysis are exploratory. Manuscript requires softening in the claimed practical value, or otherwise substantial methodological strengthening before the approach can be considered a reliable analytical tool for coffee-quality screening.

Author response: The results are now compared with standard spectroscopic methods, thus allowing for the claims presented in the manuscript. New results and comments can be seen in the manuscript.

1. All optical indicators remain semi-quantitative without calibration against an accepted metric. Manuscript states “multivariate analysis successfully differentiate the drinks” - but overall I would not agree with this. It is an interesting and original work, but remains mostly semi-quantiative and explroatory.

We compared these results with a standard instrument of absorbance – transmittance, namely the analytical Perkin Elmer Lambda 35 UV/VIS Spectrometer at the range of 400-800 nm with a scan speed of 480 nm/min. new graphs have been obtained with this spectrometer and are successfully compared with the results of the new instrument. 

2. White-light data are fitted with a dual-region exponential (Beer‐Lambert predicts linear absorbance vs concentration for homogeneous solutions). Offset term y(lambda) lacks physical justification.

We have experimentally determined an exponential dependence of the transmittance on the concentration of homogeneous solutions, which is fitted by an exponential law with R²>0.99.

Reviewer 2 Report

Comments and Suggestions for Authors

1.The work demonstrates a clear practical value, especially in the context of low-cost, in-field screening for coffee quality. However, the novelty compared to existing spectroscopy-based methods (e.g., NIR, FTIR, LIBS) could be emphasized more clearly in the Introduction and Discussion sections. Specifically, how does the proposed method uniquely complement or outperform prior low-cost approaches?

2. AS7341 is not a traditional spectrometer. Is it appropriate to define it as a miniaturized spectrometer?

3.Although the AS7341 sensor’s range is noted, a clearer explanation of how the chosen wavelengths (e.g., 445 nm, 630 nm) relate to specific coffee compounds would help bridge theory and experiment.

4. The image in the draft seems to be overexposed. Will this overexposure affect the data processing? 5. Can the spectrum of LED match that of AS7341? I see that the spectrum of white light LED is weaker around 500nm. Will it have any impact?

Author Response

Comments and Suggestions for Authors

1. The work demonstrates a clear practical value, especially in the context of low-cost, in-field screening for coffee quality. However, the novelty compared to existing spectroscopy-based methods (e.g., NIR, FTIR, LIBS) could be emphasized more clearly in the Introduction and Discussion sections. Specifically, how does the proposed method uniquely complement or outperform prior low-cost approaches?

NIR, FTIR, LIBS and other instrumental methods are precise but expensive laboratory techniques. Our method refers to portable and low cost technique, that offers the ability of transmittance or absorbance measurements, while the low cost refractometers offer only a refraction index measurement.

2. AS7341 is not a traditional spectrometer. Is it appropriate to define it as a miniaturized spectrometer?

AS7341 is able to monitor fluorescence and absorption-transmittance in specific wavelengths only. However, for presentation reasons we name it miniaturized spectrometer.

3.Although the AS7341 sensor’s range is noted, a clearer explanation of how the chosen wavelengths (e.g., 445 nm, 630 nm) relate to specific coffee compounds would help bridge theory and experiment.

AS7341 is able to measure fluorescence and absorbance-transmittance only in some wavelengths, in which we actually measured absorbance.

4. The image in the draft seems to be overexposed. Will this overexposure affect the data processing?

Measurements have been realized in dark environment and any type of possible overexposure is related to the scattering effect. Therefore, any possible overexposure is considered as an offset effect, which doesn’t affect the value of the results.

5. Can the spectrum of LED match that of AS7341? I see that the spectrum of white light LED is weaker around 500nm. Will it have any impact?

The LED spectrum is in the visible, while the detectable fluorescence and absorbance-transmittance of AS 7341 are also in the visible. In fact, the enhanced transmittance is observed at wavelengths where the LED amplitude is weaker (e.g. at 500nm) that illustrates the validity of the method and the measurement.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I recommend this manuscript to be accepted in its current form.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have responded to my concerns.